[compiler-rt][scudo] Check for failing prctl call

A bunch of MTE tests like ./ScudoUnitTest-aarch64-Test/MemtagTest.StoreTags
can fail on aarch64-linux if the kernel doesn't support the tagged address ABI. It looks like
the call to prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) can return -1, which
casted to an unsigned int and masked will return a value not equal to
PR_MTE_TCF_NONE, meaning systemDetectsMemoryTagFaultsTestOnly can return an incorrect value.

This updates the check to account for a failing prctl call.

Differential Revision: https://reviews.llvm.org/D110888