build: drop the ignore-value gnulib module

We don't need to care about very old GCC versions, so implementing the
ignore_value macro directly is not a significant burden.
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

bootstrap.conf

@@ -50,7 +50,6 @@ getpeername
 getsockname
 gettimeofday
 gnumakefile
-ignore-value
 intprops
 ioctl
 isatty

src/internal.h

@@ -63,7 +63,13 @@
 #include "libvirt/virterror.h"
 
 #include "c-strcase.h"
-#include "ignore-value.h"
+
+/* Merely casting to (void) is not sufficient since the
+ * introduction of the "warn_unused_result" attribute
+ */
+#define ignore_value(x) \
+    (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
+
 
 /* String equality tests, suggested by Jim Meyering. */
 #define STREQ(a, b) (strcmp(a, b) == 0)