setjmp is a macro.

POSIX says it's unspecified whether setjmp is a macro or a function,
but C11 says it's a macro, and the C standard always wins.

Bug: https://github.com/android-ndk/ndk/issues/744
Test: ran tests
Change-Id: I4a1abc37724f8e9d9498f2093ef3c1f3b8253949
diff --git a/libc/include/setjmp.h b/libc/include/setjmp.h
index d44946f..195f251 100644
--- a/libc/include/setjmp.h
+++ b/libc/include/setjmp.h
@@ -71,6 +71,8 @@
 int setjmp(jmp_buf __env);
 void longjmp(jmp_buf __env, int __value);
 
+#define setjmp(__env) setjmp(__env)
+
 int sigsetjmp(sigjmp_buf __env, int __save_signal_mask)
     __INTRODUCED_IN_ARM(9) __INTRODUCED_IN_MIPS(12) __INTRODUCED_IN_X86(12);
 void siglongjmp(sigjmp_buf __env, int __value)