Fix detection of include dirs with gnu compiler and non C locale
Fix detection of include dirs with gnu compiler and non C locale

Auto detection was based on parsing gcc's output so we have to
ensure that it is always 'C'.

Signed-off-by: Alexis Jeandet <cdb3ac87e0dd6c5054689b531bc30030ca920493@member.fsf.org>

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