build: Set -Qunused-arguments depending on compiler not os

This got introduced in configure.ac in
4ca6296fb7. I'll leave it there as is for
now but let's use the proper way in meson.

See discussion in https://github.com/profanity-im/profanity/pull/2090

meson.build

@@ -68,9 +68,11 @@ if is_debug
   ], language: 'c')
 endif
 
-if platform == 'osx'
+if cc.get_id() == 'clang'
   add_project_arguments('-Qunused-arguments', language: 'c')
-  
+endif
+
+if platform == 'osx'
   # Check for homebrew paths on Apple Silicon
   if run_command('test', '-d', '/opt/homebrew/include', check: false).returncode() == 0
     add_project_arguments('-I/opt/homebrew/include', language: 'c')