Disable SIGXCPU signal handling by LLVM.

Disable SIGXCPU signal handling by LLVM.

SIGXCPU is used by Mono, the C# framework used by the Unity game engine.
LLVM does not make any setrlimit(RLIMIT_CPU) calls, so when the SIGXCPU
signal is raised it is not up to LLVM to decide how to handle it.

Bug 23017372

Change-Id: I292b0eac527c5efd66022e6f75bbcb68879a30a4
Reviewed-on: https://swiftshader-review.googlesource.com/4940
Reviewed-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>