Use PNaCl's implementation of setjmp/longjmp for x86-64

PNaCl's version does not write the sandbox base address into memory.
The previous implementation also returned 0 instead of 1
when the 'val' argument was 0; PNaCl's version is correct.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4088
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/923253002