Make it work on Macintosh

[citibeth]

EasyBuild has the basic stuff needed to work on a Mac; but a number of small details thwart that effort. They are currently:

1. GCC does not build, don't know why. (Workaround is to build the toolchain via MacPorts; more on that later).

2. The Mac uses .dylib instead of .so for shared library extensions. Basic functionality for this has been put into EasyBuild, but it is not yet being used. Numerous easyconfigs and easyblocks need to be modified to fix this problem. The changes generally go as follows:
   a) In an easyblock:

   from easybuild.tools.systemtools import get_shared_lib_ext
           SHLIB_EXT = get_shared_lib_ext()
   ...use it like:   ["lib/libhdf5%s.%s" % (x,SHLIB_EXT)
   

   b) In an easyconfig: the SHLIB_EXT constant is already defined, just use as needed.

[boegel]

@citibob: thanks for reporting these issues, and for looking into fixing them (cfr. #789)!

If you have a build log to share for GCC, we may be able to help figure out what's going wrong.
Which GCC version are you trying to build? How did you work around this exactly?

OS X isn't a major target platform for EasyBuild currently since it's intended mainly for HPC systems, but we're happy to help out with getting it to work well on OS X (I am especially, since OS X is my OS of choice for my laptop).