dependencies: Always convert MinGW paths to MSVC on Windows
dependencies: Always convert MinGW paths to MSVC on Windows

The MinGW toolchain can read MinGW paths, but Python cannot and we
sometimes need to parse the libs and cflags manually (for static-only
library searching, for instance). The MinGW toolchain can always read
Windows paths with `/` as path separater, so just use that.

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