cmake: add custom shell support

[Andarwinux]

With ccache and LLVM PGO and wrapper hacks, build speed has improved so much that bash has become one of the main factors affecting the speed of building (mainly configure and autotools), so this PR add custom shell support to alleviate this problem.

The main problem is that the configure generated by autotools generates makefiles with some syntax that is not compatible with some faster POSIX shell, so we have to force use bash to execute these fucking shit.