Increase frame size for ASAN enabled builds.

This CL increases the frame size for builds where SANITIZE_TARGET is
non-empty from 6400 to 7400 (6400 was insufficient for ASAN and
coverage) to ensure that it builds successfully.

This was previously submitted as ag/1353693 for Android.common_build.mk,
but it looks like the frame size modifications have now moved to art.go
instead (found out from ag/1468464).

Bug: 30766843
Test: m test-art-host
Change-Id: If05defdcf93e2f6f7179941d95d8ee99c4c9a385