[bootstrap] Allow passing options to sub-builds for all targets

This patch makes it possible to pass a CMake option to one of the runtimes
for all targets being built. Basically, any option that starts with the
name of a runtime project being built will be forwarded as-is to the
sub-build. This is useful for customizing a sub-build for all targets.

Differential Revision: https://reviews.llvm.org/D121822

libcxx/utils/ci/run-buildbot

@@ -462,7 +462,7 @@ bootstrapping-build)
           -DLLVM_TARGETS_TO_BUILD="host" \
           -DRUNTIMES_BUILD_ALLOW_DARWIN=ON \
           -DLLVM_ENABLE_ASSERTIONS=ON \
-          -DRUNTIMES_LIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
+          -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
 
     echo "+++ Running the libc++ and libc++abi tests"
     ${NINJA} -C "${BUILD_DIR}" check-runtimes

llvm/runtimes/CMakeLists.txt

@@ -340,6 +340,17 @@ function(runtime_register_target name target)
     endforeach()
   endif()
 
+  # If we're passed any option like <project>_FOO, pass it through to the sub-builds.
+  foreach(runtime ${LLVM_ENABLE_RUNTIMES})
+    string(TOUPPER "${runtime}" runtime_upper)
+    foreach(variableName ${variableNames})
+      if (variableName MATCHES "^${runtime_upper}_.+")
+        string(REPLACE ";" "|" escaped_value "${${variableName}}")
+        list(APPEND ${name}_extra_args "-D${variableName}=${escaped_value}")
+      endif()
+    endforeach()
+  endforeach()
+
   if(NOT RUNTIMES_${name}_LLVM_ENABLE_RUNTIMES AND NOT RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES)
     string(REPLACE ";" "|" LLVM_ENABLE_RUNTIMES_PASSTHROUGH "${LLVM_ENABLE_RUNTIMES}")
     list(APPEND ${name}_extra_args -DLLVM_ENABLE_RUNTIMES=${LLVM_ENABLE_RUNTIMES_PASSTHROUGH})