[llvm] [Support] Vendor rpmalloc in-tree and use it for the Windows 64-bit release (PR #91862)

[Jay Foad via llvm-commits]

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@@ -733,7 +733,35 @@ if( WIN32 AND NOT CYGWIN )
 endif()
 set(LLVM_NATIVE_TOOL_DIR "" CACHE PATH "Path to a directory containing prebuilt matching native tools (such as llvm-tblgen)")
 
-set(LLVM_INTEGRATED_CRT_ALLOC "" CACHE PATH "Replace the Windows CRT allocator with any of {rpmalloc|mimalloc|snmalloc}. Only works with CMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded.")
+set(LLVM_ENABLE_RPMALLOC "" CACHE BOOL "Replace the CRT allocator with rpmalloc.")
+if(LLVM_ENABLE_RPMALLOC)
+  if(NOT (CMAKE_SYSTEM_NAME MATCHES "Windows|Linux"))
+    message(FATAL_ERROR "LLVM_ENABLE_RPMALLOC is only supported on Windows and Linux.")
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jayfoad wrote:

Only supported on Windows, surely? Since it relies on `LLVM_INTEGRATED_CRT_ALLOC` which is only supported on Windows (see line 767 below).

https://github.com/llvm/llvm-project/pull/91862