QStorageInfo/Linux: remove dependency on linux/mount.h

It was introduced in December 2018, which is apparently too recent for
some Linux distributions. So remove the dependency that was there only
to give us MS_RDONLY and revert to the old statfs.h / sys/vfs.h flag.

We still don't include <sys/vfs.h> because it is absent on some old
Android versions.

Amends ea6abe583f.

Pick-to: 6.7
Fixes: QTBUG-123932
Change-Id: If1bf59ecbe014b569ba1fffd17c29cc448d16358
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/io/qstorageinfo_linux.cpp

@@ -12,7 +12,6 @@
 
 #include <q20memory.h>
 
-#include <linux/mount.h>
 #include <sys/ioctl.h>
 #include <sys/statfs.h>
 
@@ -24,6 +23,11 @@
 #  define FS_IOC_GETFSLABEL     _IOR(0x94, 49, char[FSLABEL_MAX])
 #endif
 
+// or <linux/statfs.h>
+#ifndef ST_RDONLY
+#  define ST_RDONLY             0x0001  /* mount read-only */
+#endif
+
 QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
@@ -171,7 +175,7 @@ void QStorageInfoPrivate::retrieveVolumeInfo()
         bytesFree = statfs_buf.f_bfree * statfs_buf.f_frsize;
         bytesAvailable = statfs_buf.f_bavail * statfs_buf.f_frsize;
         blockSize = int(statfs_buf.f_bsize);
-        readOnly = (statfs_buf.f_flags & MS_RDONLY) != 0;
+        readOnly = (statfs_buf.f_flags & ST_RDONLY) != 0;
     }
 }