MIPS: Don't infer IRIX OS ABI from generic section names

MIPS: Don't infer IRIX OS ABI from generic section names

There are `.MIPS.abiflags', `.MIPS.options' and `.MIPS.stubs' sections
also present in Linux executables, so we can't infer IRIX OS ABI solely
from the existence of these sections.  This is not going to be a problem
as there are bound to be other sections whose names start with `.MIPS.'
in IRIX executables and this selection only matters for a non-default OS
ABI in a multiple-target GDB executable.  As a last resort the automatic
selection can be overridden with `set osabi'.

	* mips-irix-tdep.c (mips_irix_elf_osabi_sniff_abi_tag_sections):
	Exclude `.MIPS.abiflags', `.MIPS.options' and `.MIPS.stubs' from
	the list of sections determining GDB_OSABI_IRIX.