[PATCH v3 08/10] libvduse: Provide _GNU_SOURCE when compiling outside of QEMU

[Marcel Holtmann]

When the libvduse sources are used by another project, it can not be
guaranteed that _GNU_SOURCE is set by the build system. If it is for
example not set, errors like this show up.

  CC       libvduse.o
libvduse.c: In function ‘vduse_log_get’:
libvduse.c:172:9: error: implicit declaration of function ‘ftruncate’; did you 
mean ‘strncat’? [-Werror=implicit-function-declaration]
  172 |     if (ftruncate(fd, size) == -1) {
      |         ^~~~~~~~~
      |         strncat

The simplest way to allow external complication of libvduse.[ch] by
setting _GNU_SOURCE if it is not already set by the build system.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
---
 subprojects/libvduse/libvduse.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/subprojects/libvduse/libvduse.c b/subprojects/libvduse/libvduse.c
index e089d4d546cf..c871bd331a6b 100644
--- a/subprojects/libvduse/libvduse.c
+++ b/subprojects/libvduse/libvduse.c
@@ -16,6 +16,10 @@
  * later.  See the COPYING file in the top-level directory.
  */
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdbool.h>
-- 
2.38.1