powerpc/SYS.h: implement _SYSCALL_BODY() macro

[brooks]

Summary

Add _SYSCALL_BODY() macro which invokes the syscall via _SYCALL() and
calls cerror as required. Use to implement PSEUDO() and RSYSCALL().

Sponsored by: DARPA

[brooks]

lib/libc/powerpc/SYS.h

44

D43056 was missing the semicolon on this line. The compiler assertion this triggered is clearly a bug, but I wasn't able to tidy up a reproducer. (For maximum confusion, the clang reproducer doesn't reproduce the bug and instead seems to try to parse the .S file as assembly without preprocessing which goes as well as you'd expect for source that has processed includes, but not expanded macros...)