Use -fomit-frame-pointer when no debugging info is required

[Daniel Berlin]

> PS. Shouldn't DWARF-2 allow debugging anyway even for such optimizations?

Yes, but we don't produce location *lists*, which we need to.
We also don't produce the CFA info on anything but mips, mainly to save 
space.
If someone does produce the dwarf2 info needed to represent the optimized 
code, it's easier for me to make a case to someone to support it, since 
it would be such a huge benefit.
--Dan