Fix test cases/common/37 on Cygwin
Fix test cases/common/37 on Cygwin

Including newlib's <stdlib.h> brings in a '#define __has_include 0', so
using -U__has_include on the command line isn't going to remove it (so the
fallback doesn't happen and the test fails)

Instead use a '#undef __has_include' at the end of the prefix to excerise
this.

(newlib's <stdlib.h> is derived from FreeBSD, so the same problem will
probably be seen there)

pexip/meson,jpakkane/meson,jeandet/meson,becm/meson,QuLogic/meson,fmuellner/meson,aaronp24/meson,mesonbuild/meson,thiblahute/meson,QuLogic/meson,ernestask/meson,mesonbuild/meson,QuLogic/meson,trhd/meson,wberrier/meson,rhd/meson,pexip/meson,mesonbuild/meson,ernestask/meson,wberrier/meson,jeandet/meson,jeandet/meson,wberrier/meson,jpakkane/meson,becm/meson,mesonbuild/meson,jpakkane/meson,aaronp24/meson,aaronp24/meson,pexip/meson,thiblahute/meson,MathieuDuponchelle/meson,fmuellner/meson,wberrier/meson,ernestask/meson,rhd/meson,trhd/meson,MathieuDuponchelle/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,becm/meson,trhd/meson,ernestask/meson,becm/meson,MathieuDuponchelle/meson,trhd/meson,fmuellner/meson,becm/meson,rhd/meson,fmuellner/meson,MathieuDuponchelle/meson,ernestask/meson,mesonbuild/meson,QuLogic/meson,thiblahute/meson,jeandet/meson,rhd/meson,MathieuDuponchelle/meson,mesonbuild/meson,wberrier/meson,aaronp24/meson,thiblahute/meson,mesonbuild/meson,MathieuDuponchelle/meson,aaronp24/meson,ernestask/meson,aaronp24/meson,ernestask/meson,trhd/meson,pexip/meson,pexip/meson,rhd/meson,QuLogic/meson,jpakkane/meson,ernestask/meson,pexip/meson,rhd/meson,becm/meson,wberrier/meson,jpakkane/meson,MathieuDuponchelle/meson,fmuellner/meson,becm/meson,mesonbuild/meson,jeandet/meson,pexip/meson,trhd/meson,fmuellner/meson,thiblahute/meson,thiblahute/meson,pexip/meson,thiblahute/meson,MathieuDuponchelle/meson,jpakkane/meson,becm/meson,thiblahute/meson,pexip/meson,trhd/meson,aaronp24/meson,jeandet/meson,trhd/meson,wberrier/meson,aaronp24/meson,thiblahute/meson,QuLogic/meson,jeandet/meson,QuLogic/meson,rhd/meson,pexip/meson,becm/meson,aaronp24/meson,fmuellner/meson,rhd/meson,mesonbuild/meson,jeandet/meson,trhd/meson,jeandet/meson,jpakkane/meson,MathieuDuponchelle/meson,fmuellner/meson,jpakkane/meson,fmuellner/meson,QuLogic/meson,wberrier/meson,ernestask/meson,becm/meson