Fixed Mac OS X 10.7 as a build platform (for GCC 4).

* Use gcc and g++ rather than cc and c++, as the latter now point to
  clang with recent Xcode versions and compilation of the host tools
  fail for various reasons with it.
* Replace the case-sensitive filesystem check with a more basic one,
  as diskutil no longer supports the behaviour of getting info for the
  volume that any path is on.
* Updated ReadMe with a correct list of prerequisites for OS X.
* GCC 2 builds are still broken due to a strange error that only
  occurs with a GCC 2 built on OS X 10.7

ReadMe

@@ -75,6 +75,13 @@ The following darwin ports need to be installed:
  * libiconv
  * gnuregex
  * gsed
+ * cdrtools
+ * yasm
+ * wget
+ * less
+ * mpfr
+ * gmp
+ * libmpc
 
 More information about individual distributions of Linux and BSD can be found
 at http://haiku-os.org/guides/building/pre-reqs