diff --git a/src/ci/docker/host-x86_64/arm-android/Dockerfile b/src/ci/docker/host-x86_64/arm-android/Dockerfile
index add2647fa1e..30dd2380132 100644
--- a/src/ci/docker/host-x86_64/arm-android/Dockerfile
+++ b/src/ci/docker/host-x86_64/arm-android/Dockerfile
@@ -31,7 +31,7 @@ ENV TARGETS=arm-linux-androideabi
 
 ENV RUST_CONFIGURE_ARGS --arm-linux-androideabi-ndk=/android/ndk/arm-14
 
-ENV SCRIPT python3 ../x.py --stage 2 test --target $TARGETS
+ENV SCRIPT python3 ../x.py --stage 2 test --host '' --target $TARGETS
 
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
diff --git a/src/ci/docker/host-x86_64/armhf-gnu/Dockerfile b/src/ci/docker/host-x86_64/armhf-gnu/Dockerfile
index f1ccbc928a7..1dc86496358 100644
--- a/src/ci/docker/host-x86_64/armhf-gnu/Dockerfile
+++ b/src/ci/docker/host-x86_64/armhf-gnu/Dockerfile
@@ -79,6 +79,6 @@ COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
 ENV RUST_CONFIGURE_ARGS --qemu-armhf-rootfs=/tmp/rootfs
-ENV SCRIPT python3 ../x.py --stage 2 test --target arm-unknown-linux-gnueabihf
+ENV SCRIPT python3 ../x.py --stage 2 test --host '' --target arm-unknown-linux-gnueabihf
 
 ENV NO_CHANGE_USER=1
diff --git a/src/ci/docker/host-x86_64/disabled/asmjs/Dockerfile b/src/ci/docker/host-x86_64/disabled/asmjs/Dockerfile
index 6335dc089b2..4f16854dc61 100644
--- a/src/ci/docker/host-x86_64/disabled/asmjs/Dockerfile
+++ b/src/ci/docker/host-x86_64/disabled/asmjs/Dockerfile
@@ -34,7 +34,7 @@ ENV EMCC_CFLAGS=-O1
 # Emscripten installation is user-specific
 ENV NO_CHANGE_USER=1
 
-ENV SCRIPT python3 ../x.py --stage 2 test --target $TARGETS
+ENV SCRIPT python3 ../x.py --stage 2 test --host '' --target $TARGETS
 
 # This is almost identical to the wasm32-unknown-emscripten target, so
 # running with assertions again is not useful
diff --git a/src/ci/docker/host-x86_64/disabled/dist-x86_64-redox/Dockerfile b/src/ci/docker/host-x86_64/disabled/dist-x86_64-redox/Dockerfile
index b32c498c74e..108ed65c5b5 100644
--- a/src/ci/docker/host-x86_64/disabled/dist-x86_64-redox/Dockerfile
+++ b/src/ci/docker/host-x86_64/disabled/dist-x86_64-redox/Dockerfile
@@ -19,4 +19,4 @@ ENV \
     CXX_x86_64_unknown_redox=x86_64-unknown-redox-g++
 
 ENV RUST_CONFIGURE_ARGS --enable-extended
-ENV SCRIPT python3 ../x.py dist --target x86_64-unknown-redox
+ENV SCRIPT python3 ../x.py dist --host '' --target x86_64-unknown-redox
diff --git a/src/ci/docker/host-x86_64/dist-android/Dockerfile b/src/ci/docker/host-x86_64/dist-android/Dockerfile
index 6d38e199564..051e7976522 100644
--- a/src/ci/docker/host-x86_64/dist-android/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-android/Dockerfile
@@ -32,7 +32,7 @@ ENV RUST_CONFIGURE_ARGS \
       --x86_64-linux-android-ndk=/android/ndk/x86_64-21 \
       --disable-docs
 
-ENV SCRIPT python3 ../x.py dist --target $TARGETS
+ENV SCRIPT python3 ../x.py dist --host '' --target $TARGETS
 
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
diff --git a/src/ci/docker/host-x86_64/dist-i586-gnu-i586-i686-musl/Dockerfile b/src/ci/docker/host-x86_64/dist-i586-gnu-i586-i686-musl/Dockerfile
index 995f7c301f8..bc6ecce2567 100644
--- a/src/ci/docker/host-x86_64/dist-i586-gnu-i586-i686-musl/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-i586-gnu-i586-i686-musl/Dockerfile
@@ -47,5 +47,5 @@ ENV CFLAGS_i586_unknown_linux_musl=-Wa,-mrelax-relocations=no
 ENV TARGETS=i586-unknown-linux-gnu,i686-unknown-linux-musl
 
 ENV SCRIPT \
-      python3 ../x.py --stage 2 test --target $TARGETS && \
-      python3 ../x.py dist --target $TARGETS,i586-unknown-linux-musl
+      python3 ../x.py --stage 2 test --host '' --target $TARGETS && \
+      python3 ../x.py dist --host '' --target $TARGETS,i586-unknown-linux-musl
diff --git a/src/ci/docker/host-x86_64/dist-various-1/Dockerfile b/src/ci/docker/host-x86_64/dist-various-1/Dockerfile
index 431892697d4..38ca708aa48 100644
--- a/src/ci/docker/host-x86_64/dist-various-1/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-various-1/Dockerfile
@@ -187,8 +187,8 @@ ENV RUST_CONFIGURE_ARGS \
       --disable-docs
 
 ENV SCRIPT \
-      python3 ../x.py --stage 2 test --target $RUN_MAKE_TARGETS src/test/run-make && \
-      python3 ../x.py dist --target $TARGETS
+      python3 ../x.py --stage 2 test --host '' --target $RUN_MAKE_TARGETS src/test/run-make && \
+      python3 ../x.py dist --host '' --target $TARGETS
 
 # sccache
 COPY scripts/sccache.sh /scripts/
diff --git a/src/ci/docker/host-x86_64/dist-various-2/Dockerfile b/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
index 3081f29aef2..e940454c292 100644
--- a/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
@@ -110,4 +110,4 @@ ENV RUST_CONFIGURE_ARGS --enable-extended --enable-lld --disable-docs \
   --set target.wasm32-wasi.wasi-root=/wasm32-wasi \
   --musl-root-armv7=/musl-armv7
 
-ENV SCRIPT python3 ../x.py dist --target $TARGETS
+ENV SCRIPT python3 ../x.py dist --host '' --target $TARGETS
diff --git a/src/ci/docker/host-x86_64/test-various/Dockerfile b/src/ci/docker/host-x86_64/test-various/Dockerfile
index 8c606d88d68..14e516370f5 100644
--- a/src/ci/docker/host-x86_64/test-various/Dockerfile
+++ b/src/ci/docker/host-x86_64/test-various/Dockerfile
@@ -41,7 +41,7 @@ ENV RUST_CONFIGURE_ARGS \
 ENV NO_DEBUG_ASSERTIONS=1
 
 ENV WASM_TARGETS=wasm32-unknown-unknown
-ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --target $WASM_TARGETS \
+ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --host '' --target $WASM_TARGETS \
   src/test/run-make \
   src/test/ui \
   src/test/compile-fail \
@@ -50,13 +50,13 @@ ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --target $WASM_TARGETS \
   library/core
 
 ENV NVPTX_TARGETS=nvptx64-nvidia-cuda
-ENV NVPTX_SCRIPT python3 /checkout/x.py --stage 2 test --target $NVPTX_TARGETS \
+ENV NVPTX_SCRIPT python3 /checkout/x.py --stage 2 test --host '' --target $NVPTX_TARGETS \
   src/test/run-make \
   src/test/assembly
 
 ENV MUSL_TARGETS=x86_64-unknown-linux-musl \
     CC_x86_64_unknown_linux_musl=x86_64-linux-musl-gcc \
     CXX_x86_64_unknown_linux_musl=x86_64-linux-musl-g++
-ENV MUSL_SCRIPT python3 /checkout/x.py --stage 2 test --target $MUSL_TARGETS
+ENV MUSL_SCRIPT python3 /checkout/x.py --stage 2 test --host '' --target $MUSL_TARGETS
 
 ENV SCRIPT $WASM_SCRIPT && $NVPTX_SCRIPT && $MUSL_SCRIPT
diff --git a/src/ci/docker/host-x86_64/wasm32/Dockerfile b/src/ci/docker/host-x86_64/wasm32/Dockerfile
index b4c783c781b..25c0bdf110e 100644
--- a/src/ci/docker/host-x86_64/wasm32/Dockerfile
+++ b/src/ci/docker/host-x86_64/wasm32/Dockerfile
@@ -53,7 +53,7 @@ ENV NO_CHANGE_USER=1
 
 # FIXME: Re-enable these tests once https://github.com/rust-lang/cargo/pull/7476
 # is picked up by CI
-ENV SCRIPT python3 ../x.py test --stage 2 --target $TARGETS \
+ENV SCRIPT python3 ../x.py test --stage 2 --host '' --target $TARGETS \
     --exclude library/core \
     --exclude library/alloc \
     --exclude library/proc_macro \
diff --git a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-8/Dockerfile b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-8/Dockerfile
index 0c9d6ed442e..34c6396b7b5 100644
--- a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-8/Dockerfile
+++ b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-8/Dockerfile
@@ -45,7 +45,7 @@ ENV SCRIPT python2.7 ../x.py --stage 2 test --exclude src/tools/tidy && \
            # on the `x86_64` host when they're built as `armv5te` binaries.
            # (we're only interested in the MIR output, so this doesn't matter)
            python2.7 ../x.py --stage 2 test src/test/mir-opt --pass=build \
-                                  --target=armv5te-unknown-linux-gnueabi && \
+                             --host='' --target=armv5te-unknown-linux-gnueabi && \
            # Run the UI test suite again, but in `--pass=check` mode
            #
            # This is intended to make sure that both `--pass=check` continues to