Decoupling -O from -fvia-C

I think it is again time to discuss whether -O should still imply - 
fvia-C.

I have recently committed a few patches that allow the NCG to compile  
the RTS. Position-independent code works in the NCG on Darwin/x86 and  
(almost untested) on Linux/x86, but will never work in for -fvia-C  
compilation. So now there are situations where -fasm is required, and  
there are fewer and fewer situations where -fvia-C is required.

The Makefile in compiler/ adds -O to the HC_OPTS for some files,  
which overrides any global -fasm, so compiling a libHSghc_dyn.dylib  
(or .so) requires editing the Makefile.

The only argument for having -O imply -fvia-C that I am aware of is  
that -fvia-C code is slightly faster than -fasm on x86. This was not  
even the case on PowerPC, last time I checked.

I rest my case.

Cheers,

	Wolfgang