to compile blender with gcc on IRIX, IRIX_USE_GCC needs to be set to true in
user-def.mk.
Other changes related to irix:
* compile solid from extern/
* don't build plugins (yet) with "make release" when using gcc (the shell
script used assumes MIPSpro is installed)
* use statvfs instead of statfs on irix, like done on solaris
* use external libs from $(LCGDIR) instead of /usr/freeware
* use glew header files from $(LCGDIR)/glew instead of the ones installed on
the system (this applies to other platforms as well)
* ffmpeg support currently is disabled on irix
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