Hi,

The gdb.base/dump.exp test had a few failures for MIPS N64. That is 
expected since SREC, IHEX and TEKHEX dump formats don't support 64-bit 
addresses, and MIPS N64 uses them.

Skipping this test for MIPS is not the right thing as some ABI's are 
32-bit and so should be tested against the usual set of SREC, IHEX and 
TEKHEX formats.

The attached patch checks for the N64 ABI and sets the internal flag 
is64bitonly accordingly, skipping the SREC, IHEX and TEKHEX tests.

Ok?