gdb.base/gnu-ifunc.exp doesn't fail gracefully on targets that don't 
support this feature -- on nios2-linux-gnu I've seen TCL errors from 
trying to copy the nonexistent shared library that fails to build to the 
target.

I see that ld/testsuite/ld-ifunc/ifunc.exp explicitly lists all the 
targets where IFUNC is expected to work, but it seemed more maintainable 
to me to tweak these gdb tests to pay attention to the return status 
from trying to build the test cases.  Is this OK to commit?

-Sandra