libcxx 'LLVM_USE_SANITIZER=Address;Undefined'

[modocache]

Summary

Allow users to simultaneously enable address and undefined behavior
sanitizers, in the same manner that LLVM's 'HandleLLVMOptions.cmake'
allows.

Prior to this patch, cmake -DLLVM_USE_SANITIZER="Address;Undefined"
would succeed and the build would build most of the LLVM project with
-fsanitize=address,undefined, but a warning would be printed by
libcxx's CMake, and the build would use neither sanitizer. This
patch results in no warning being printed, and both sanitizers are used
in building libcxx.

[jroelofs]

LGTM

[ldionne]

@modocache We have a libcxx review group that gets added as a blocking reviewer on libcxx patches automatically, that's for a reason. Please don't commit without an approval from the group anymore.

The patch looks good to me.

libcxx/CMakeLists.txt

if (USE_SANITIZER STREQUAL "Address")
       append_flags(SANITIZER_FLAGS "-fsanitize=address")
     elseif (USE_SANITIZER MATCHES "Memory(WithOrigins)?")
       append_flags(SANITIZER_FLAGS -fsanitize=memory)
       if (USE_SANITIZER STREQUAL "MemoryWithOrigins")
         append_flags(SANITIZER_FLAGS "-fsanitize-memory-track-origins")
       endif()
     elseif (USE_SANITIZER STREQUAL "Undefined")
       append_flags(SANITIZER_FLAGS "-fsanitize=undefined -fno-sanitize=vptr,function -fno-sanitize-recover=all")
+    elseif (USE_SANITIZER STREQUAL "Address;Undefined" OR
+            USE_SANITIZER STREQUAL "Undefined;Address")
+      append_flags(SANITIZER_FLAGS "-fsanitize=address,undefined -fno-sanitize=vptr,function -fno-sanitize-recover=all")
     elseif (USE_SANITIZER STREQUAL "Thread")
       append_flags(SANITIZER_FLAGS -fsanitize=thread)
     else()
       message(WARNING "Unsupported value of LLVM_USE_SANITIZER: ${USE_SANITIZER}")
     endif()
   elseif(USE_SANITIZER AND MSVC)
     message(WARNING "LLVM_USE_SANITIZER is not supported on this platform.")
   endif()