[Support] Make building with snmalloc work

Differential revision: https://reviews.llvm.org/D87471

Author: zmodem

llvm/lib/Support/CMakeLists.txt

@@ -65,7 +65,6 @@ if(LLVM_INTEGRATED_CRT_ALLOC)
     add_definitions(-DENABLE_OVERRIDE -DENABLE_PRELOAD)
     set(ALLOCATOR_FILES "${LLVM_INTEGRATED_CRT_ALLOC}/rpmalloc/rpmalloc.c")
   elseif(LLVM_INTEGRATED_CRT_ALLOC MATCHES "snmalloc$")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17" PARENT_SCOPE)
     set(ALLOCATOR_FILES "${LLVM_INTEGRATED_CRT_ALLOC}/src/override/malloc.cc" "${LLVM_INTEGRATED_CRT_ALLOC}/src/override/new.cc")
     set(system_libs ${system_libs} "mincore.lib" "-INCLUDE:malloc")
   elseif(LLVM_INTEGRATED_CRT_ALLOC MATCHES "mimalloc$")
@@ -249,6 +248,18 @@ endif()
 
 set_property(TARGET LLVMSupport PROPERTY LLVM_SYSTEM_LIBS "${llvm_system_libs}")
 
+
+if(LLVM_INTEGRATED_CRT_ALLOC)
+  if(LLVM_INTEGRATED_CRT_ALLOC MATCHES "snmalloc$")
+    set_property(TARGET LLVMSupport PROPERTY CXX_STANDARD 17)
+    add_definitions(-D_SILENCE_CXX17_ITERATOR_BASE_CLASS_DEPRECATION_WARNING)
+    if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" AND
+        "${CMAKE_SYSTEM_PROCESSOR}" MATCHES "x86_64")
+      set_property(TARGET LLVMSupport PROPERTY COMPILE_FLAGS "-mcx16")
+    endif()
+  endif()
+endif()
+
 if(LLVM_WITH_Z3)
   target_include_directories(LLVMSupport SYSTEM
     PRIVATE