diff --git a/src/librustc_ast/build.rs b/src/librustc_ast/build.rs
deleted file mode 100644
index 9b861f96409..00000000000
--- a/src/librustc_ast/build.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");
-    println!("cargo:rerun-if-env-changed=CFG_DISABLE_UNSTABLE_FEATURES");
-}
diff --git a/src/librustc_attr/build.rs b/src/librustc_attr/build.rs
deleted file mode 100644
index 863f2b7337b..00000000000
--- a/src/librustc_attr/build.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_RELEASE");
-    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");
-}
diff --git a/src/librustc_codegen_llvm/build.rs b/src/librustc_codegen_llvm/build.rs
deleted file mode 100644
index d1fc624c689..00000000000
--- a/src/librustc_codegen_llvm/build.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_VERSION");
-    println!("cargo:rerun-if-env-changed=CFG_PREFIX");
-    println!("cargo:rerun-if-env-changed=CFG_LLVM_ROOT");
-}
diff --git a/src/librustc_codegen_ssa/build.rs b/src/librustc_codegen_ssa/build.rs
deleted file mode 100644
index ea2af6e192e..00000000000
--- a/src/librustc_codegen_ssa/build.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");
-}
diff --git a/src/librustc_driver/build.rs b/src/librustc_driver/build.rs
deleted file mode 100644
index 414d13445f0..00000000000
--- a/src/librustc_driver/build.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_RELEASE");
-    println!("cargo:rerun-if-env-changed=CFG_VERSION");
-    println!("cargo:rerun-if-env-changed=CFG_VER_DATE");
-    println!("cargo:rerun-if-env-changed=CFG_VER_HASH");
-}
diff --git a/src/librustc_incremental/build.rs b/src/librustc_incremental/build.rs
deleted file mode 100644
index d230ba91039..00000000000
--- a/src/librustc_incremental/build.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_VERSION");
-}
diff --git a/src/librustc_interface/build.rs b/src/librustc_interface/build.rs
deleted file mode 100644
index 79a343e0fee..00000000000
--- a/src/librustc_interface/build.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=RUSTC_INSTALL_BINDIR");
-}
diff --git a/src/librustc_llvm/build.rs b/src/librustc_llvm/build.rs
index 78e27b10ec6..f00bd7d47f0 100644
--- a/src/librustc_llvm/build.rs
+++ b/src/librustc_llvm/build.rs
@@ -163,7 +163,7 @@ fn main() {
         cfg.define(&flag, None);
     }
 
-    println!("cargo:rerun-if-changed-env=LLVM_RUSTLLVM");
+    println!("cargo:rerun-if-env-changed=LLVM_RUSTLLVM");
     if env::var_os("LLVM_RUSTLLVM").is_some() {
         cfg.define("LLVM_RUSTLLVM", None);
     }
diff --git a/src/librustc_metadata/build.rs b/src/librustc_metadata/build.rs
deleted file mode 100644
index 7d5c58ecea2..00000000000
--- a/src/librustc_metadata/build.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_VERSION");
-    println!("cargo:rerun-if-env-changed=CFG_VIRTUAL_RUST_SOURCE_BASE_DIR");
-}
diff --git a/src/librustc_middle/build.rs b/src/librustc_middle/build.rs
deleted file mode 100644
index af7723aea34..00000000000
--- a/src/librustc_middle/build.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-use std::env;
-
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_LIBDIR_RELATIVE");
-    println!("cargo:rerun-if-env-changed=CFG_COMPILER_HOST_TRIPLE");
-    println!("cargo:rerun-if-env-changed=RUSTC_VERIFY_LLVM_IR");
-
-    if env::var_os("RUSTC_VERIFY_LLVM_IR").is_some() {
-        println!("cargo:rustc-cfg=always_verify_llvm_ir");
-    }
-}
diff --git a/src/librustc_session/session.rs b/src/librustc_session/session.rs
index 4ad95e95e9a..1b8f6cdd8be 100644
--- a/src/librustc_session/session.rs
+++ b/src/librustc_session/session.rs
@@ -548,7 +548,7 @@ impl Session {
         self.opts.debugging_opts.asm_comments
     }
     pub fn verify_llvm_ir(&self) -> bool {
-        self.opts.debugging_opts.verify_llvm_ir || cfg!(always_verify_llvm_ir)
+        self.opts.debugging_opts.verify_llvm_ir || option_env!("RUSTC_VERIFY_LLVM_IR").is_some()
     }
     pub fn borrowck_stats(&self) -> bool {
         self.opts.debugging_opts.borrowck_stats
diff --git a/src/librustc_target/build.rs b/src/librustc_target/build.rs
deleted file mode 100644
index 368200b776d..00000000000
--- a/src/librustc_target/build.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_DEFAULT_LINKER");
-}