glib2 OSX: add try_compiler_option_strictly

In OSX, Command Line Tools 5.1's default compiler is clang.
So, '-Wout-of-line-declaration' causes flood of warnings as follows:

```
warning: unknown warning option '-Wunsafe-loop-optimizations'; did you
mean
      '-Wout-of-line-declaration'? [-Wunknown-warning-option]
```