cmake2meson: convert varexp to lowercase
cmake2meson: convert varexp to lowercase

since variable names in 'set' statements are converted to lowercase, the
variable itself should be converted to lower-case too when used.

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