[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:

I know for certain that I ran into a lot of issues back in the days where we used the `LLVM_ENABLE_PROJECTS` build caused by the rest of LLVM sneaking in flags via these kinds of CMake files. This is actively harmful. I think it's much better to remove it if we can, and normally our CI would tell us if we missed something.

So I'd support making the naive change that takes us closer to where we should be, and then figuring out where we went wrong in case it breaks something. You can always blame it on me :)

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