build-style/meson: update for new env var behaviour
build-style/meson: update for new env var behaviour

meson 0.54 now honors _FOR_BUILD env vars, and we don't have to set CC
and friends to the host system vars. Setting PKG_CONFIG_FOR_BUILD is
needed since otherwise it would pickup our cross wrapper

necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages