elf/tst-rtld-does-not-exist: Pass --inhibit-cache to rtld

This avoids a test failure when the system has no /etc/ld.so.cache.

Tested on x86_64-linux-gnu.

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>