The cache-line configure test uses FILE, fopen(), fscanf(), and fclose()
before stdio.h is included.  Modern compilers reject the implicit declarations,
so the test always falls back to a hard-coded 64-byte cache line.

Patch both the m4 source and the generated configure script because the release
tarball ships generated build machinery and the ebuild deliberately avoids
autoreconf with its obsolete Automake version.

--- a/m4/acx_cache_line.m4
+++ b/m4/acx_cache_line.m4
@@ -59,4 +59,4 @@ size_t cache_line_size() {
 #elif defined(linux)
-
+#include <stdio.h>
 size_t cache_line_size() {
     FILE * p = 0;
--- a/configure
+++ b/configure
@@ -27211,4 +27211,4 @@ size_t cache_line_size() {
 #elif defined(linux)
-
+#include <stdio.h>
 size_t cache_line_size() {
     FILE * p = 0;