[llvm] [llvm] Disable HandleLLVMOptions in runtimes mode (PR #73031)

[Louis Dionne via llvm-commits]

================
@@ -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)
----------------
ldionne wrote:

@michaelrj-google Any thoughts about libc?

Basically, I want to avoid creating a haunted graveyard around these flags. We all agree they're undesirable and can be harmful, so let's do our best to remove them and see what needs to be fixed in addition. Let's not do the easy thing (this PR as-is) because it just sweeps future problems under the rug.

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