SpiderMonkey upgrade details

Latest revision: 5ecd532a167e

Grab latest SpiderMonkey source:

cd ~/mozilla-central
make -C objdir/js/src source-package
cd ~/servo/src/support/mozjs
rm -rf .
cp ~/mozilla-central/objdir/mozjs-31.0.1.tar.bz2 .
tar xvjf mozjs-31.0.1.tar.bz2 --strip 1

Upgrade bindgen:

• Check out external copy of LLVM, follow clang instructions
• Update to last official revision used by Servo's Rust's copy
• Check out revisions of compiler-rt and clang that are from approximately the same date as official revision
• Compile LLVM and clang
• Add a symlink to the newly built libclang.so and libclang.a sitting in rust-bindgen's working dir
• Find a revision of bindgen that builds with Servo's current rustc
• Build bindgen with Servo's rustc with -L.