https://bugs.gentoo.org/906533
--- a/m4/as-unaligned-access.m4
+++ b/m4/as-unaligned-access.m4
@@ -19,6 +19,7 @@ AC_DEFUN([AS_UNALIGNED_ACCESS], [
   fi
   if test x"$as_cv_unaligned_access" = x ; then
     AC_TRY_RUN([
+#include <string.h>
 int main(int argc, char **argv)
 {
   char array[] = "ABCDEFGH";
--- a/configure
+++ b/configure
@@ -12022,6 +12022,7 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+#include <string.h>
 int main(int argc, char **argv)
 {
   char array[] = "ABCDEFGH";