meson: remove obsolete check for LOOP_CTL_GET_FREE

The LOOP_CTL_GET_FREE constant was introduced to Linux in

  commit 770fe30a46a12b6fb6b63fbe1737654d28e84844
  Author: Kay Sievers <kay.sievers@vrfy.org>
  Date:   Sun Jul 31 22:08:04 2011 +0200

    loop: add management interface for on-demand device allocation

This is old enough that all our supported platforms can be assumed
to have this feature. As a plus point, this meson check is going
to start failing with future GCC. It fails to set _GNU_SOURCE, thus
'unshare' is not defined by the header, and its relying on an
implicit function decl. For added fun this whole meson check was
semantically insane because LOOP_CTL_GET_FREE is not a valid arg
to unshare().

Fixes https://fedoraproject.org/wiki/Toolchain/PortingToModernC
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/util/virfile.c

@@ -750,8 +750,6 @@ int virFileUpdatePerm(const char *path,
 
 #if defined(__linux__) && WITH_DECL_LO_FLAGS_AUTOCLEAR
 
-# if WITH_DECL_LOOP_CTL_GET_FREE
-
 /* virFileLoopDeviceOpenLoopCtl() returns -1 when a real failure has occurred
  * while in the process of allocating or opening the loop device.  On success
  * we return 0 and modify the fd to the appropriate file descriptor.
@@ -795,7 +793,6 @@ static int virFileLoopDeviceOpenLoopCtl(char **dev_name, int *fd)
     *dev_name = looppath;
     return 0;
 }
-# endif /* WITH_DECL_LOOP_CTL_GET_FREE */
 
 static int virFileLoopDeviceOpenSearch(char **dev_name)
 {
@@ -864,7 +861,6 @@ static int virFileLoopDeviceOpen(char **dev_name)
 {
     int loop_fd = -1;
 
-# if WITH_DECL_LOOP_CTL_GET_FREE
     if (virFileLoopDeviceOpenLoopCtl(dev_name, &loop_fd) < 0)
         return -1;
 
@@ -872,7 +868,6 @@ static int virFileLoopDeviceOpen(char **dev_name)
 
     if (loop_fd >= 0)
         return loop_fd;
-# endif /* WITH_DECL_LOOP_CTL_GET_FREE */
 
     /* Without the loop control device we just use the old technique. */
     loop_fd = virFileLoopDeviceOpenSearch(dev_name);