[compiler-rt] Fix MSVC /external detection in cmake scripts

As suggested by https://reviews.llvm.org/D116872#4650507

Differential Revision: https://reviews.llvm.org/D116872

Author: aganea

compiler-rt/lib/asan/CMakeLists.txt

@@ -92,7 +92,7 @@ append_rtti_flag(OFF ASAN_CFLAGS)
 
 # Silence warnings in system headers with MSVC.
 if(NOT CLANG_CL)
-  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external /external:W0 /external:anglebrackets" ASAN_CFLAGS)
+  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external;/external:W0;/external:anglebrackets" ASAN_CFLAGS)
 endif()
 
 # Too many existing bugs, needs cleanup.

compiler-rt/lib/interception/CMakeLists.txt

@@ -21,7 +21,7 @@ append_rtti_flag(OFF INTERCEPTION_CFLAGS)
 
 # Silence warnings in system headers with MSVC.
 if(NOT CLANG_CL)
-  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external /external:W0 /external:anglebrackets" INTERCEPTION_CFLAGS)
+  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external;/external:W0;/external:anglebrackets" INTERCEPTION_CFLAGS)
 endif()
 
 add_compiler_rt_object_libraries(RTInterception

compiler-rt/lib/ubsan/CMakeLists.txt

@@ -57,7 +57,7 @@ append_list_if(SANITIZER_CAN_USE_CXXABI -DUBSAN_CAN_USE_CXXABI UBSAN_CXXFLAGS)
 
 # Silence warnings in system headers with MSVC.
 if(NOT CLANG_CL)
-  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external /external:W0 /external:anglebrackets" UBSAN_CXXFLAGS)
+  append_list_if(COMPILER_RT_HAS_EXTERNAL_FLAG "/experimental:external;/external:W0;/external:anglebrackets" UBSAN_CXXFLAGS)
 endif()
 
 set(UBSAN_LINK_FLAGS ${SANITIZER_COMMON_LINK_FLAGS})