[GWP-ASan] 32-bit test pointers, allow multi-init for test.
GWP-ASan test currently fail on 32-bit platforms, as some of the pointers are
larger than uintptr_t on 32-bit platforms. Fix up all those instances.
Also add an uncompress varint test where the result is an underflow.
Furthermore, allow multi-init for testing. Each gtest when running
check-gwp_asan apparently runs in its own instance, but when integrating
these tests into Android, this behaviour isn't the same. We remove the
global multi-init check here, to allow for testing to work elsewhere, and we're
not really worried about multi-init anyway as it's part of our contract with
Reviewers: eugenis, vlad.tsyrklevich
Reviewed By: eugenis
Subscribers: #sanitizers, llvm-commits, pcc
Tags: #sanitizers, #llvm
Differential Revision: https://reviews.llvm.org/D71121