f32 values passed on the stack would previously cause an assertion in
unpackFromMemLoc.. This would only trigger in the presence of the F extension
making f32 a legal type. Otherwise the f32 would be legalized.
This patch fixes that by keeping LocVT=f32 when a float is passed on the
stack. It also adds test coverage for this case, and tests that also
demonstrate lw/sw/flw/fsw will be selected when most profitable. i.e. there is
no unnecessary i32<->f32 conversion in registers.
llvm-svn: 343756