new llvmgcc4 snapshop

This should build with mainline, includes some performance tweaks, better build support for mingw, detects a faulty --enable-llvm configure option, and has better support for the Darwin/X86 ABI:


Any functional changes for non-Darwin or am I ok continuing to use the
last snapshop?


Last snapshot is fine. This one will produce better performing code for some bitfield accesses, and has improvements for mingw/darwin x86.