GCC 11 build fixes

GCC 11 build fixes

Some files used std::numeric_limits without including <limits> and
failed to compile.

Some dynamic casts and calls to AndroidHardwareBufferExternalApi::
getInstance() produced nonnull warnings. Suppress these by
wrapping them in if statements.

This commit also removes implicit-fallthrough from the list of ignored
GCC warnings in check_build_sanity.py. All such warnings in the CTS
should be fixed by now and recent versions of Clang also support
this warning.

VK-GL-CTS issue: 2842

Change-Id: I5bd290f9c312a30c2fcb223307c7b5c785a0fa92