Fix exclusion overriding local integer_overflow.

INTEGER_OVERFLOW_EXCLUDE_PATHS should only apply to the global sanitizer
setting, and should not override local module settings. This pulls out
the check so it occurs earlier and does not interfere with local
settings. This makes Make consistent with Soong's behavior as well.

Bug: 30969751
Test: Created a test build file with this explicitly set, excluded the
path, and checked if it was still being sanitized.

Change-Id: I9020d92bae136b6087d37f71d5337acaefe850b4