Darwin GCC-5.3-based bootstrap compilers

These are intended as "minimal" compiler packages to enable folks to build their own compilers using the source branches here (and elsewhere). If there's significant demand, I can build "full" toolchains supporting C-family,Fortran and Ada.

---

These packages install to /opt/iains//darwin-gcc-5.3r0
They do not reference anything outside that directory (other than standard system libraries).
They can be uninstalled by removing that directory.

---

For all platforms:

You need to have the latest XCode (for the system version you're installing on) with command line tools installed (on versions of OS X for which that's a relevant distinction) so that the system SDKs, includes and libraries are available.

---

The release is based on:
https://github.com/iains/darwin-gcc-5 as per tag (using gmp-6.1, mpfr-3.1.3, mpc-1.0.3)

For Darwin9 -- Darwin13 (OS X 10.5 -- 10.9):
we add:
https://github.com/iains/darwin-xtools 1.0.0 (based on cctools-877.5 and ld64-253.3)
https://github.com/iains/llvm-project llvm-only - based off SVN 256450 (to build libLTO.dylib).

The i686-darwin9 toolchain may be used on i686-darwin9+ (OS X 10.5+)
The x86_64-darwin10 toolchain may be used on x86_64-darwin10..13 (OS X 10.6 - 10.9)
The x86_64-darwin14 toolchain may be used on x86_64-darwin14+ (OS X 10.10+)
The powerpc-darwin9 toolchain may be used on powerpc-darwin9. (OS X 10.5)

If you only want C, C++ or Ada - these toolchains will work "out of the tin". If you want more/other languages - you can use them as a starting point; So, supposing you want to build C, ObjectiveC, Fortran, and Ada on x86_64-darwin12, you could use the x86_64-darwin10 as a starting point (since it supports Ada) - and follow the plan in "https://github.com/iains/darwin-toolchains-start-here".

Note that you could use the xtools-based toolchains on Darwin14/15 (OS X 10.10/11), but XCode 7.2 has newer editions of the system tools, so there's probably not too many reasons to do so.