[X86] Fix CodeGen Module Flag for -mibt-seal

When assertions are enabled, clang will perform RoundTrip for CompilerInvocation argument generation. ibt-seal flags are currently missing in this argument generation, and because of that, the feature doesn't get enabled for these cases. Performing RoundTrip is the default for assert builds, rendering the feature broken in these scenarios.

This patch fixes this and adds a test to properly verify that modules are  being generated with the flag when -mibt-seal is used.

Please, add any known relevant reviewer which I may have missed.

[1] - https://reviews.llvm.org/D116070

Reviewed By: pengfei, gftg, aaron.ballman, nickdesaulniers

Differential Revision: https://reviews.llvm.org/D118052