Fix MSVC backend crashes when `c_pch` or `cpp_pch` is not an array
Fix MSVC backend crashes when `c_pch` or `cpp_pch` is not an array

pexip/meson,pexip/meson,jeandet/meson,becm/meson,QuLogic/meson,thiblahute/meson,jeandet/meson,thiblahute/meson,QuLogic/meson,mesonbuild/meson,jpakkane/meson,becm/meson,jpakkane/meson,QuLogic/meson,pexip/meson,MathieuDuponchelle/meson,becm/meson,mesonbuild/meson,MathieuDuponchelle/meson,becm/meson,MathieuDuponchelle/meson,jeandet/meson,mesonbuild/meson,QuLogic/meson,MathieuDuponchelle/meson,jpakkane/meson,becm/meson,jpakkane/meson,jpakkane/meson,MathieuDuponchelle/meson,mesonbuild/meson,pexip/meson,jeandet/meson,jeandet/meson,becm/meson,thiblahute/meson,jeandet/meson,pexip/meson,jpakkane/meson,mesonbuild/meson,QuLogic/meson,mesonbuild/meson,jeandet/meson,pexip/meson,becm/meson,pexip/meson,MathieuDuponchelle/meson,becm/meson,QuLogic/meson,mesonbuild/meson,pexip/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,mesonbuild/meson,thiblahute/meson,thiblahute/meson,jeandet/meson,jpakkane/meson,QuLogic/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,jeandet/meson,thiblahute/meson,becm/meson,pexip/meson,QuLogic/meson,pexip/meson,MathieuDuponchelle/meson,QuLogic/meson,thiblahute/meson,thiblahute/meson,mesonbuild/meson,thiblahute/meson,becm/meson