Fix building on OS X 10.9 Maverics (clang-500.2.79) with Homebrew

Description of the fixes introduced:
* GCC 2.95.3 is now being compiled using -std=gnu89 flag. Otherwise the compilation fails during linking phase with "undefined symbols for architecture i386: \_is_reserved_word"
* In binutils package, LLVM complained about multiple incompatible declarations of xexit(), failing with error. The declarations are now coherent for both binutils *and* GCC and based on the GCC header file.
* fd2fsd used install -D option, which doesn't exist on BSD install. I replaced the appropriate block with separate find/install calls.
* build\_libnix() now uses multi-core make call - performance improvement