Add missing register preserve in x86/x86_64 longjmp.

Change-Id: I3fc442f819229640e9c0ec4f9c865d9bf0e70881
diff --git a/libc/arch-x86/bionic/setjmp.S b/libc/arch-x86/bionic/setjmp.S
index 8a2f30c..86e6e3c 100644
--- a/libc/arch-x86/bionic/setjmp.S
+++ b/libc/arch-x86/bionic/setjmp.S
@@ -151,9 +151,11 @@
 
   PIC_PROLOGUE
   pushl %eax
+  pushl %ecx
   pushl (_JB_SIGFLAG * 4)(%edx)
   call PIC_PLT(__bionic_setjmp_cookie_check)
   addl $4,%esp
+  popl %ecx
   popl %eax
   PIC_EPILOGUE