meson: fix keymaps without qemu-keymap

In case the qemu-keymap tool generating them is neither installed on the
system nor built from sources (due to xkbcommon not being available)
qemu will not find the keymaps when started directly from the build
tree,

This happens because commit ddcf607fa3 ("meson: drop keymaps symlink")
removed the symlink to the source tree, and the special handling for
install doesn't help in case we do not install qemu.

Lets fix that by simply copying over the file from the source tree as
fallback.

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20200827102617.14448-1-kraxel@redhat.com>
[thuth: Rebased, changed "config_host['qemu_datadir']" to "qemu_datadir",
        added Gerd's UNLINK fix to configure script]
Signed-off-by: Thomas Huth <thuth@redhat.com>

configure

@@ -8065,6 +8065,9 @@ fi
 # so the build tree will be missing the link back to the new file, and
 # tests might fail. Prefer to keep the relevant files in their own
 # directory and symlink the directory instead.
+# UNLINK is used to remove symlinks from older development versions
+# that might get into the way when doing "git update" without doing
+# a "make distclean" in between.
 DIRS="tests tests/tcg tests/tcg/lm32 tests/qapi-schema tests/qtest/libqos"
 DIRS="$DIRS tests/qtest tests/qemu-iotests tests/vm tests/fp tests/qgraph"
 DIRS="$DIRS docs docs/interop fsdev scsi"
@@ -8081,6 +8084,7 @@ LINKS="$LINKS .gdbinit scripts" # scripts needed by relative path in .gdbinit
 LINKS="$LINKS tests/acceptance tests/data"
 LINKS="$LINKS tests/qemu-iotests/check"
 LINKS="$LINKS python"
+UNLINK="pc-bios/keymaps"
 for bios_file in \
     $source_path/pc-bios/*.bin \
     $source_path/pc-bios/*.elf \
@@ -8101,6 +8105,11 @@ for f in $LINKS ; do
         symlink "$source_path/$f" "$f"
     fi
 done
+for f in $UNLINK ; do
+    if [ -L "$f" ]; then
+        rm -f "$f"
+    fi
+done
 
 (for i in $cross_cc_vars; do
   export $i

pc-bios/keymaps/meson.build

@@ -38,19 +38,29 @@ if meson.is_cross_build() or 'CONFIG_XKBCOMMON' not in config_host
 else
   native_qemu_keymap = qemu_keymap
 endif
+
 t = []
 foreach km, args: keymaps
+  if native_qemu_keymap.found()
+    # generate with qemu-kvm
     t += custom_target(km,
                        build_by_default: true,
                        output: km,
                        command: [native_qemu_keymap, '-f', '@OUTPUT@', args.split()],
                        install_dir: qemu_datadir / 'keymaps')
+  else
+    # copy from source tree
+    t += custom_target(km,
+                       build_by_default: true,
+                       input: km,
+                       output: km,
+                       command: ['cp', '@INPUT@', '@OUTPUT@'],
+                       install_dir: qemu_datadir / 'keymaps')
+  endif
 endforeach
-if t.length() > 0
+
+if native_qemu_keymap.found()
   alias_target('update-keymaps', t)
-else
-  # install from the source tree
-  install_data(keymaps.keys(), install_dir: qemu_datadir / 'keymaps')
 endif
 
 install_data(['sl', 'sv'], install_dir: qemu_datadir / 'keymaps')