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

[James Henderson via llvm-commits]

================
@@ -14,6 +14,20 @@ function(add_llvm_target_unittest test_dir_name)
   add_llvm_unittest(${test_dir_name} DISABLE_LLVM_LINK_LLVM_DYLIB ${ARGN})
 endfunction()
 
+# gtest macros like EXPECT_TRUE are expanded to a single line
+# multi-statement code with if/else. eg:
+#   if (...)
+#     EXPECT_TURE(...)
+# will be expanded into something like:
+#   if(...)
+#     switch (0) case 0: default: if (...) ; else return;;
+# GCC may emit false positive dangling-else warnings for such code.
+# However, such warnings are actually against LLVM's style guide.
+# disable the warning for GCC so that one can enbable Werror.
----------------
jh7370 wrote:

`disable` -> `Disable`
`enbable` -> `enable`

I'd also do `Werror` -> `-Werror` to make it clear that this is an option.

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