testsuite: Skip target not support -pthread [PR104676].

testsuite: Skip target not support -pthread [PR104676].

The "ftree-parallelize-loops=" imply -pthread option in gcc/gcc.cc,
some target are not support pthread like elf target use newlib,
and will get an error:

"*-*-elf-gcc: error: unrecognized command-line option '-pthread'"

so we add an additional condition "{target pthread}" to make sure the
dg-additional-options runs on support targets.

gcc/testsuite/ChangeLog

	PR target/104676
	* gcc.dg/torture/pr104676.c: Add "{target pthread}" check.