[PATCH, MIPS] Calling convention differs depending on the presence of MSA

[Sameera Deshpande]

Hi Matthew,

Please find attached the patch to fix the calling convention issue, 
where argument and result passing convention differed for MSA and 
non-MSA variants.

The implementation of TARGET_RETURN_IN_MEMORY is altered to block V4SF to be returned in registers.

Ok for trunk?

- Thanks and regards,
  Sameera D.


Changelog:
gcc/
    * config/mips/mips.c (mips_return_in_memory) : Restrict V4SFmode to be returned in registers.

gcc/testsuite/
    * gcc.target/mips/msa-fp-cc.c : New testcase.