Fix unix/Makefile to build on OSX
Force OSX to compile with clang even if gcc is available
Change LDFLAGS syntax to be compatible with clang
Fix questionable syntax on line 90
Remove extraneous tab character
Incorporate change in assignment logic suggested by dhylands
Clean up logical flow for setting LDFLAGS to build for Linux and OSX
Add more specific comments describing what is going on.
Merge pull request #871 from blmorris/osx_build_fix

Fix unix/Makefile to build on OSX