compiler supports ifunc but musl dynamic linker does not.

--- ./configure.orig
+++ ./configure
@@ -1787,7 +1787,8 @@
 int main(void) { foo(); return 0; }
 EOF
 if compile_prog "-mavx2" "" ; then
-    if readelf --syms $TMPE |grep "IFUNC.*foo" >/dev/null 2>&1; then
+    if readelf --syms $TMPE |grep "IFUNC.*foo" >/dev/null 2>&1 &&
+       ldd $TMPE >/dev/null 2>&1; then
         avx2_opt="yes"
     fi
 fi