MIPS: Fix Irix gas testcases about pdr section

  * testsuite/gas/elf/elf.exp (section2): Add -mpdr option to assembler command line for mips-irix targets.
  * testsuite/gas/mips/elf-rel26.d: Add -mpdr command line option.
  * testsuite/gas/mips/mips16-e.d: Likewise.
  * testsuite/gas/mips/mips16-f.d: Likewise.
  * testsuite/gas/mips/mips16-hilo-match.d: Likewise.
  * testsuite/gas/mips/mips16-e-irix.d: Likewise.
  * testsuite/gas/mips/call-nonpic-1.d: Adjust regexp to allow for mips-irix targets.
  * testsuite/gas/mips/irix-no-pdr.d: New test file.
  * testsuite/gas/mips/mips.exp: Run new test for mips-irix targets.