mangler and runtime updates for gcc 4 on ia64

Gcc 4 is doing more clever optimizations than earlier gccs.
These changes let ghc compile and run on ia64 with gcc 4.0.3.

Register stack frames are enlarged so that all functions use the
same size stack frame.
The code to mangle tail calls has been cleaned up and made more
general.
Additional floating-point and special-purpose registers used by
GCC are saved upon entering the STG runtime.
More general handling of NOP instructions.
Handling of functions with multiple epilogues or no epilogue.