musl: meson: check existence of renameat2()

musl-1.2.5 does not provide renameat2(). Note, it is added by
05ce67fea9,
hence hopefully it will be provided by musl-1.2.6 or newer.

meson.build

@@ -579,6 +579,7 @@ assert(long_max > 100000)
 conf.set_quoted('LONG_MAX_STR', f'@long_max@')
 
 foreach ident : [
+        ['renameat2',         '''#include <stdio.h>'''],        # since musl-1.2.6
         ['set_mempolicy',     '''#include <sys/syscall.h>'''],  # declared at numaif.h provided by libnuma, which we do not use
         ['get_mempolicy',     '''#include <sys/syscall.h>'''],  # declared at numaif.h provided by libnuma, which we do not use
         ['strerrorname_np',   '''#include <string.h>'''],       # since glibc-2.32

src/include/musl/stdio.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include_next <stdio.h>
+
+#if !HAVE_RENAMEAT2
+#  define RENAME_NOREPLACE (1 << 0)
+#  define RENAME_EXCHANGE  (1 << 1)
+#  define RENAME_WHITEOUT  (1 << 2)
+
+int missing_renameat2(int __oldfd, const char *__old, int __newfd, const char *__new, unsigned __flags);
+#  define renameat2 missing_renameat2
+#endif

src/libc/musl/meson.build

@@ -3,3 +3,7 @@
 if get_option('libc') != 'musl'
         subdir_done()
 endif
+
+libc_wrapper_sources += files(
+        'stdio.c',
+)

src/libc/musl/stdio.c

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <stdio.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#if !HAVE_RENAMEAT2
+int missing_renameat2(int __oldfd, const char *__old, int __newfd, const char *__new, unsigned __flags) {
+        return syscall(__NR_renameat2, __oldfd, __old, __newfd, __new, __flags);
+}
+#endif