Update FileCheck prefixes in preparation for the addition of Mips64 MSA tests.

No functional changes.
[ASan] Move the SIGSEGV/SIGBUS handling to sanitizer_common

This change is a part of refactoring intended to have common signal handling behavior in all tools.
This particular CL moves InstallSignalHandlers() into sanitizer_common (making it InstallDeadlySignalHandlers()), but doesn't enable default signal handlers for any tool other than ASan.