Patch specifies that DJGPP do not have mmap() even when sys/mman.h is available.
libbacktrace is perhaps currently unusable for DJGPP but otherwise mmap() usability
misdetection breaks cross-compiler build for DJGPP target (for example Linux hosted
cross-compiler)

Andris

2015-12-05 Andris Pavenis <andris.pavenis@iki.fi>

* configure.ac: Specify that DJGPP do not have mmap even when sys/mman.h exists
* configure: Regenerate