easy-builder: always sync before doing serious things to prevent issues happening...

easy-builder: always sync before doing serious things to prevent issues happening with slow I/O on macOS

errors like that:

> CMakeFiles/gtktheme-mojave.dir/build.make:73: CMakeFiles/gtkglext.dir/build.make:73: CMakeFiles/gtktheme-mojave.dir/progress.make: No such file or directory

> ginstall: cannot change permissions of 'netradiant/build/lib/gtkglext-1.0/include/gdkglext-config.h': No such file or directory

> mkdir: netradiant/build/registry: Operation not permitted

> clang: error: no such file or directory: '../../libs/libcm.a'