[CMake] [MinGW] Enable use of LLVM_USE_SANITIZER in a MinGW environment

Currently using LLVM_USE_SANITIZER with a MinGW target leads to a fatal
configuration error due to an unsupported platform. MinGW targets on
clang however implement a few sanitizers, currently ASAN and UBSAN.

This patch enables LLVM_USE_SANITIZER in a MinGW environment as well.

Differential Revision: https://reviews.llvm.org/D95750

Author: zero9178

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -793,6 +793,21 @@ if(LLVM_USE_SANITIZER)
     else()
       message(FATAL_ERROR "Unsupported value of LLVM_USE_SANITIZER: ${LLVM_USE_SANITIZER}")
     endif()
+  elseif(MINGW)
+    if (LLVM_USE_SANITIZER STREQUAL "Address")
+      append_common_sanitizer_flags()
+      append("-fsanitize=address" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    elseif (LLVM_USE_SANITIZER STREQUAL "Undefined")
+      append_common_sanitizer_flags()
+      append("${LLVM_UBSAN_FLAGS}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    elseif (LLVM_USE_SANITIZER STREQUAL "Address;Undefined" OR
+            LLVM_USE_SANITIZER STREQUAL "Undefined;Address")
+      append_common_sanitizer_flags()
+      append("-fsanitize=address" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+      append("${LLVM_UBSAN_FLAGS}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    else()
+      message(FATAL_ERROR "This sanitizer not yet supported in a MinGW environment: ${LLVM_USE_SANITIZER}")
+    endif()
   elseif(MSVC)
     if (LLVM_USE_SANITIZER STREQUAL "Address")
       append_common_sanitizer_flags()