CCache requires this flag when building with precompiled headers.
Without it, the preprocessor fails and CCache fallbacks to running the
real compiler.
Users still need to set 'sloppiness' to 'pch_defines,time_macros' in
their ccache.conf file for CCache to cache builds that use precompiled
headers. See the CCache manual for more info:
https://ccache.samba.org/manual.html#_precompiled_headers
In addition to filtering libs out while generating the command-line, we
must also filter them out in find_library() otherwise these libs will be
detected as "found" on Windows with MSVC.
Closes https://github.com/mesonbuild/meson/issues/1509
Gabríel Arthúr Pétursson