[test, x86] Fix spurious x86-target-features.c failure

x86-target-features.c can spuriously fail when checking for absence of
the string "lvi" in the compiler output due to the temporary path used
for the output file. For example:
"-o" "/tmp/lit-tmp-981j7lvi/x86-target-features-670b86.o"
will make the test fail. This commit checks specifically for lvi as a
target feature, in a similar way to the positive CHECK directive just
above.

Test Plan: fails when using -mlvi-hardening and pass otherwise

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D125084