testsuite: Adjust switch-exp-transform-3.c for 32bit

32bit x86 CPUs won't natively support the FFS operation on a 64 bit
type.  Therefore, I'm setting the long long int part of the
switch-exp-transform-3.c test to only execute with 64bit targets.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/switch-exp-transform-3.c: Set the long long
	int test to only execute with 64bit targets.

Signed-off-by: Filip Kastl <fkastl@suse.cz>