Hopefully fix the build on crazy libc implementations.



git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/libobjc2/trunk@36110 72102866-910b-0410-8b05-ffd578937521
Merge remote-tracking branch 'upstream/master'
Bumped _XOPEN_SOURCE to include stpcpy() definition.
Removed hard coded PAGE_SIZE definition.
Fixed mkstemp() usage.