Toolchain packaging

[springmeyer]

I'm planning on attempting to package - for both OS X and Linux - my ideal c++ toolchain in a portable way.

This would be the latest:

• llvm
• clang
• lldb
• include-what-you-use
• compiler-rt for the latest and greatest sanitizers
• clang-extra-tools

These would be built using c++11 (--enable-cxx11) and on OS X (at least) linking libc++ (--enable-libcpp)

Things this would unlock:

• easy for new C++ developers to get setup without fighting with homebrew installs or apt-get installs
• recent enough binaries such that:
  • --coverage works on linux
  • the thread sanitizer works on os x
  • lldb --batch works on os x
• make it possible to write scripts on top of the toolchain: one example would be a simple batch script that 1) runs a program that is crashing, and 2) generates a backtrace. This would be useful because so many differences exist between OS X and Linux in how core files work and how backtraces are generated with gdb and lldb, so a simple script to make this seamless across systems would boost productivity.

Steps to get there:

• Test building toolchain from source on travis: https://github.com/springmeyer/build-llvm
• Write mason package
• Make tweaks to build (likely lots needed) to ensure it is portable
  • how to handle python/swig dependency with lldb
  • how to handle libedit dependency with lldb
  • how to handle c++ library dependency - package libc++ statically?

/cc @kkaefer @GretaCB @lbud

[springmeyer]

done in #452