Magic patch from bug 933336
Bug 936312: Adjust tests' assumptions about B2G's WebGL support.
Bug 942290: Merge ARM exidx info with DWARF if both are present.
Import Chromium seccomp-bpf stuff, rev 799ae3bd3edd1801fee3dcf721269fa0864067f7
First attempt at using the Chromium sandbox codegen for our stuff
Slight fixup
Add missing chromium-imported file
Migrate seccomp sandbox filter to SandboxAssembler
Flatten out the old macro maze
Remove most of the explicitly arch-tested whitelist items.

Many of them are large-file issues, or otherwise seem to be better
expressed as tests for the existence of a syscall.
Minor cleanup
Handle socketcall-muxed syscalls correctly (I hope)
fixup typo
That doesn't need to be ifdef'ed
Fixup for "Minor cleanup"