[llvm] [NFC] [CMake] Add -Wno-dangling-else for GCC built unittests (PR #112817)

[Jinsong Ji via llvm-commits]

================
@@ -14,6 +14,11 @@ function(add_llvm_target_unittest test_dir_name)
   add_llvm_unittest(${test_dir_name} DISABLE_LLVM_LINK_LLVM_DYLIB ${ARGN})
 endfunction()
 
+# GCC may emit false positive warnings against LLVM's style guide.
----------------
jsji wrote:

Sure. Done. Thanks @teresajohnson !

https://github.com/llvm/llvm-project/pull/112817