Fix llvm.prefetch instrinct for old LLVM versions

Seems the last parameter to llvm.prefectch was added in LLVM 3.0.
Always have LLVM optimize globals

This pass is pretty cheap and eliminates the aliases generated by the LLVM
backend. This in turn is required for dynamic linking to work correctly,
as LLVM fails to properly attribute calls to aliased addresses.
Remove spurious extra brace in LLVM metadata

This actually caused a segfault in the optimized stage 2 compiler due to
wrong TBAA data.