fix(bootstrap): allow failure

Author: JayAndJef

src/bootstrap/src/core/sanity.rs

@@ -391,6 +391,7 @@ $ pacman -R cmake && pacman -S mingw-w64-x86_64-cmake
 /// checks if the compiler at `path` is clang by looking at defined macros
 fn is_clang_compiler(path: PathBuf, build: &Build) -> bool {
     let cc_output = command(&path)
+        .allow_failure()
         .arg("-E") // preprocess only
         .arg("-dM") // dump defines
         .arg("-x")