Specify architecture for SPARC gas tests

[Jose E. Marchesi]

    > The hwcaps tags are not created in Solaris though, so that's why the
    > tests are failing...  I wonder if it is possible to change the tests so
    > they use -msparc:MACH only when testing in solaris targets?
    
    I've no idea, but there's already tcl code that modifies/rewrites tags
    in the *.?d files.  That could certainly be extended...

I just checked and you can set OBJDUMPFLAGS before running
run_dump_test.  What about doing something like this in sparc.exp:

proc set_tests_arch {arch} {
  global OBJDUMPFLAGS

  if [istarget "sparc-solaris*"] {
     set OBJDUMPFLAGS "-msparc:$arch"
  }
}

[...]

set_tests_mach v9m8
run_dump_test "on"
run_list_test "on-diag" "-64"
; ... other M8 tests

set_tests_mach v9m
run_dump_test "xcrypto"
; ... other M7 tests

wdyt?