testsuite: Fix up pr107541.c test

The test fails when long is 32-bit rather than 64-bit (say x86_64 with
RUNTESTFLAGS='--target_board=unix\{-m32,-m64\} tree-ssa.exp=pr107541.c'
).
I've tweaked it to use long long so it passes even on the 32-bit
targets, and added an early out for weirdo targets because I think
the test assumes the usual 1/2/4/8 bytes sizes for char/short/int/long long.

2022-11-09  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/107541
	* gcc.dg/tree-ssa/pr107541.c (c): Use long long type rather than long.
	(main): Punt if sizeof short isn't 2, or int 4, or long long 8.