Fix bug when memtag_heap in diag but not sanitizers

Without this we get:
unsupported argument 'memtag_heap' to option '-fno-sanitize-trap='
(cherry picked from https://android-review.googlesource.com/q/commit:2a6762605574d6fbcea63e9d5e18d184e241417d)

Bug: 286415307
Merged-In: Iaeb23d0f4962bb3d788036fadc14b9420221a38e
Change-Id: Iaeb23d0f4962bb3d788036fadc14b9420221a38e