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

Port non-upstreamed patches forward:

• https://github.com/mozilla-servo/mozjs/commit/307dd4bd397100a5446fb3d8d5868fc052577d3a
• https://github.com/mozilla-servo/mozjs/commit/bfe6b9544ff0df852bdca16a68770b9381e5f35c
• https://github.com/mozilla-servo/mozjs/commit/81aeed0b6159acdedf7dd530fb6c3bde5ddbb70a
• https://github.com/mozilla-servo/mozjs/commit/2f49752829e5cf68b68caee62c338a7c989c7992

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.