Work around IA64 tst-setcontext2.c compile failure.

Work around IA64 tst-setcontext2.c compile failure.

Building tests for IA64 runs into a build failure compiling
stdlib/tst-setcontext2.c:

tst-setcontext2.c: In function 'do_test':
tst-setcontext2.c:210:20: error: passing argument 1 of 'sigismember' from incompatible pointer type [-Werror=incompatible-pointer-types]
   if (sigismember (&oldctx.uc_sigmask, SIGUSR2) != 1)
                    ^

Indeed, the IA64 uc_sigmask as unsigned long rather than the larger
userspace sigset_t.  Fixing this might be hard; this patch works
around the build failure by making IA64 wrap the test with a version
that #defines sigismember to add a cast (I'd welcome a better approach
for fixing this).

Tested (compilation only) for ia64.

	* sysdeps/unix/sysv/linux/ia64/tst-setcontext2.c: New file.