macos: link static libc++ when building stage2

With this change, it is now possible to use zig-bootstrap as the
initial C/C++ compiler, and then build stage2 with the resultant
stage1 without the need to link any system libs!
6c3050e3c3Jakub Konka committed on 5/13/2021, 5:55:59 AMparentfb8527b
1 file changedLine totals unavailable