eglfs: Put Linux-specific includes within Q_OS_LINUX guards.

This should fix the build on platforms like the BSDs, where linux/fb.h does
not exist.

Change-Id: Ia06403d71c3aaa0e177c85dcefa7986647777ae0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/platforms/eglfs/qeglfshooks_stub.cpp

@@ -44,10 +44,12 @@
 #include <QtPlatformSupport/private/qeglconvenience_p.h>
 #include <QtCore/QRegularExpression>
 
+#if defined(Q_OS_LINUX)
 #include <fcntl.h>
 #include <unistd.h>
 #include <linux/fb.h>
 #include <sys/ioctl.h>
+#endif
 
 #include <private/qcore_unix_p.h>