[llvm] [llvm] Disable some LLVM arguments in runtimes mode (PR #73031)

[Louis Dionne via llvm-commits]

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@@ -151,6 +151,9 @@ endif()
 # Avoid checking whether the compiler is working.
 set(LLVM_COMPILER_CHECKED ON)
 
+# This can be used to detect whether we're in the runtimes build.
+set(LLVM_RUNTIMES_BUILD ON)
+
 # Handle common options used by all runtimes.
 include(AddLLVM)
 include(HandleLLVMOptions)
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ldionne wrote:

We could add the `include` in compiler-rt and in libc if we expect those to rely on it perhaps? For libc++, libc++abi and libunwind, I am fairly confident that if we remove it and our CI doesn't break, we're okay. It might break something, but if that's the case and if it's actively being used then we have pretty good systems in place to fix it quickly, and I'm willing to take responsibility to fix it.

https://github.com/llvm/llvm-project/pull/73031