Accept 128 + SIGNAL as well as SIGNAL as valid
returns for fork/exec tests.
Also, make changes so that test compiles in opensource. Test
had compile errors on latest Ubuntu 16.04 image with updated bazel to
3.4.0 (as well as base 2.0) used for Kokoro tests.
PiperOrigin-RevId: 327510310
Add a decent set of syscall tests for rseq(2). These are a bit awkward because
of issues with library integration. libc may register rseq on thread start
(including before main on the initial thread), precluding much testing. Thus we
run tests in a libc-free subprocess.
Support for rseq(2) in gVisor will come in a later commit.
PiperOrigin-RevId: 284595994
