Remove more BSD cruft from the public headers.

Change-Id: I1e3097f745b526db448bf72fbc05fb2ba23929a0
diff --git a/libm/freebsd-compat.h b/libm/freebsd-compat.h
index 1481cc2..a4dd6c2 100644
--- a/libm/freebsd-compat.h
+++ b/libm/freebsd-compat.h
@@ -26,6 +26,8 @@
 #define __strong_reference(sym,aliassym) \
     extern __typeof (sym) aliassym __attribute__ ((__alias__ (#sym)))
 
+#define __warn_references(sym,msg) /* ignored */
+
 /* digittoint is in BSD's <ctype.h>. */
 int digittoint(char ch);