Limit Linux-only code with Q_OS_LINUX

The QStorageInfo/QStorageIterator implementation used for Linux is used also
on Hurd, as it uses an interface provided by GNU libc.
QStorageIterator::device() tries to use PATH_MAX (unavailable on the Hurd)
to lookup a /dev/block/ path, which exists on Linux only; hence, perform that
check within a Q_OS_LINUX block.
Forwarded: no
Last-Update: 2020-04-19

Gbp-Pq: Name qstorageinfo_linux.diff

src/corelib/io/qstorageinfo_unix.cpp

@@ -566,6 +566,7 @@ inline QByteArray QStorageIterator::fileSystemType() const
 
 inline QByteArray QStorageIterator::device() const
 {
+#ifdef Q_OS_LINUX
     // check that the device exists
     if (mnt.mnt_fsname[0] == '/' && access(mnt.mnt_fsname, F_OK) != 0) {
         // It doesn't, so let's try to resolve the dev_t from /dev/block.
@@ -581,6 +582,7 @@ inline QByteArray QStorageIterator::device() const
             return dev;
         }
     }
+#endif
     return QByteArray(mnt.mnt_fsname);
 }