RFC -- targets with unsigned bifields

[Jeff Law <jlaw@ventanamicro.com>]

So mcore-elf is the slowest target to test with a simulator.  Not 
because it's simulator is particularly bad, but because some tests 
timeout as they've gotten into infinite loops.  This causes the 
mcore-elf port to take about 2X longer than most other gdbsim ports.

I tracked this down to the port unconditionally adding 
-funsigned-bitfields to CC1_SPEC.  According to the comment it's how the 
ABI is defined for the mcore targets.

It'd be nice to get reasonable results from mcore-elf in a reasonable 
amount of time.  The question is how.

I *could* just disable the -funsigned-bitfields within the tester.  We 
certainly have the ability to carry forward patches like this which 
exist only to help the testing effort.

Another approach would be to add an explicit -fsigned-bifields to the 
arguments for the affected tests.  I'd guess it's on the order of around 
35 distinct tests that would need to be updated.

A third approach would be to grub around and see if there's a way to add 
a -fsigned-bitfields using dejagnu, perhaps in the baseboards file.

Looking for suggestions/recommendations here.

Jeff