make __getauxval a public ABI symbol

This is needed so that libgcc can access AT_HWCAP without violating
link namespace rules.

Internally musl already used __getauxval symbol for the same reason,
we just remove the hidden marking.

src/include/sys/auxv.h

@@ -5,6 +5,6 @@
 
 #include <features.h>
 
-hidden unsigned long __getauxval(unsigned long);
+unsigned long __getauxval(unsigned long);
 
 #endif