native libc detection: respect spaces in CC env var

Zig has detection for when it is accidentally being called recursively
when trying to find the native libc installation. However it was not
working, resulting in a cryptic failure, because zig tried to execute
a command which had spaces in it rather than tokenizing it.

This improves the user experience of `zig cc` for systems that Zig
does not support cross-compiling for.

Closes #8960
c230258d9bAndrew Kelley committed on 6/10/2021, 5:20:52 PMparent2d0dff6
1 file changedLine totals unavailable