meson: define _GNU_SOURCE to detect copy_file_range() (#7734)

Follow-up for bad7a0c81f501fbbcc79af9eaa4b8254441c4a1f of git
repository for glibc.

Recently glibc added `copy_file_range()`, but to use it,
`_GNU_SOURCE` needs to be defined. This adds the flag in
meson.build to detect the function by meson correctly.

diff --git a/meson.build b/meson.build
index be8e610..f3a65b3 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -468,7 +468,8 @@ foreach ident : [
         ['kcmp',              '''#include <linux/kcmp.h>'''],
         ['keyctl',            '''#include <sys/types.h>
                                  #include <keyutils.h>'''],
-        ['copy_file_range',   '''#include <sys/syscall.h>
+        ['copy_file_range',   '''#define _GNU_SOURCE
+                                 #include <sys/syscall.h>
                                  #include <unistd.h>'''],
         ['bpf',               '''#include <sys/syscall.h>
                                  #include <unistd.h>'''],