[committed 0/3] MIPS/GAS: R6 PC-relative relocation fixes

[Maciej W. Rozycki]

Hi,

 I have committed this small set of patches to address issues in GAS with 
resolved R6 PC-relative relocations.  Such relocations are expected to be 
produced from certain pre-R6 code containing ISA override directives, 
however GAS terminates with assertion failures instead, which is something 
that is supposed not to happen with any user-supplied code.

 Each change is self-contained, however only the final one allows affected 
code to assemble succesfully and hence it's only with that change that 
test cases are included.  See individual commit descriptions for further 
details about each change.

 A further improvement can be made to BFD_RELOC_MIPS_19_PCREL_S2 and 
BFD_RELOC_MIPS_19_PCREL_S2 expression validity checks, and also constants 
are handled not exactly right, at least with REL targets.  I'll take care 
of this separately later.

  Maciej