fix clobber of edx in i386 vsyscall asm

this function does not obey the normal calling convention; like a
syscall instruction, it's expected not to clobber any registers except
the return value. clobbering edx could break callers that were reusing
the value cached in edx after the syscall returns.

src/internal/i386/syscall.s

@@ -16,7 +16,8 @@ __vsyscall:
 	mov 12(%esp),%edi
 	push %eax
 	call 1f
-2:	pop %ebx
+2:	mov %ebx,%edx
+	pop %ebx
 	pop %ebx
 	pop %edi
 	ret