llvm: llvm 5.0 is released and the current stable
llvm: llvm 5.0 is released and the current stable

So set it as the first versioned config to check for, and add
llvm-config-6.0 to the list of configs.

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