Allows instrumentation of Minix components using LLVM passes from
"llvm-apps" repository
In addition, the change does the following:
1. Move releasetools/generate_gold_plugin.sh to minix/llvm
2. Move external/bsd/llvm/passes to minix/llvm/passes
3. libLTO.so, LLVMgold.so and WeakAliasModuleOverride.so files
now get installed in minix/llvm/bin
In case of installation of both clang and GCC, we want to be able to
switch which one is the default by adapting the cc, c++ & cpp symlinks.
The default behaviour implemented here is to prefer clang over gcc if
they are both installed.
Change-Id: Ic14720cd876d2bf934d345a955cb5789378209e6
