Merge pull request apple#32918 from nathawes/make-libcxx-build-a-noop

[build-script-impl] Simplify libcxx build step

utils/build-script-impl

@@ -1661,19 +1661,11 @@ for host in "${ALL_HOSTS[@]}"; do
                 ;;
 
             libcxx)
-                build_targets=(cxx-headers)
+                build_targets=()
                 cmake_options=(
                     "${cmake_options[@]}"
-                    -DCMAKE_C_FLAGS="$(llvm_c_flags ${host})"
-                    -DCMAKE_CXX_FLAGS="$(llvm_c_flags ${host})"
-                    -DCMAKE_C_FLAGS_RELWITHDEBINFO="-O2 -DNDEBUG"
-                    -DCMAKE_CXX_FLAGS_RELWITHDEBINFO="-O2 -DNDEBUG"
-                    -DCMAKE_BUILD_TYPE:STRING="${LLVM_BUILD_TYPE}"
-                    -DLLVM_INCLUDE_DOCS:BOOL=TRUE
-                    -DLLVM_CONFIG_PATH="$(build_directory "${LOCAL_HOST}" llvm)/bin/llvm-config"
                     "${llvm_cmake_options[@]}"
                 )
-
                 ;;
 
             swift)
@@ -2303,6 +2295,10 @@ for host in "${ALL_HOSTS[@]}"; do
                 call env "${EXTRA_DISTCC_OPTIONS[@]}" "${CMAKE}" "${cmake_options[@]}" "${EXTRA_CMAKE_OPTIONS[@]}" "${source_dir}"
         fi
 
+        if [[ "${product}" == "libcxx" ]]; then
+            continue
+        fi
+
         # When we are building LLVM create symlinks to the c++ headers. We need
         # to do this before building LLVM since compiler-rt depends on being
         # built with the just built clang compiler. These are normally put into