ld: Pass $NOPIE_CFLAGS and $NOPIE_LDFLAGS to test pr21964-4

ld: Pass $NOPIE_CFLAGS and $NOPIE_LDFLAGS to test pr21964-4

Linker test "pr21964-4" fails on s390x on Ubuntu 24.10 but not on
Fedora 41.  The reason is that GCC on Ubuntu is configured with
--enable-default-pie, so that it defaults to compile with -fPIE
and link with -pie, which causes the test to erroneously fail.

ld/testsuite/
	PR ld/21090
	* ld-elf/shared.exp: Compile pr21964-4 with $NOPIE_CFLAGS and
	link with $NOPIE_LDFLAGS.

Bug: https://sourceware.org/PR21090
Signed-off-by: Jens Remus <jremus@linux.ibm.com>