strcmp() with optimization level > 1 is broken on Emscripten (!)

Trivial workaround that should eventually go to the quirks file
until this is fixed in Emscripten.

test/default/cmptest.h

@@ -26,6 +26,14 @@
 # define rand(X) arc4random(X)
 #endif
 
+#ifdef __EMSCRIPTEN__
+# define strcmp(s1, s2) xstrcmp(s1, s2)
+int strcmp(const char *s1, const char *s2) {
+    while (*s1 == *s2++) { if (*s1++ == 0) return 0; }
+    return *(unsigned char *) s1 - *(unsigned char *) --s2;
+}
+#endif
+
 FILE *fp_res;
 int   xmain(void);