Fix the build with more standards-compliant compilers such as GCC 4.7. [1]
On the way replace USE_GMAKE by USES=gmake.
PR: 184566 [1], 182136
Submitted by: Christoph Moench-Tegeder <cmt@burggraben.net> [1]
Approved by: maintainer (Jason Bacon <jwbacon@tds.net>) [1]