Fix Cygwin compatibility – part III

Commit 65504c8 misplaced the #endif.
The definition of _GNU_SOURCE is only needed for Cygwin.

Defining _GNU_SOURCE on Linux results in compiler warnings because this
macro is already defined by the compiler.

Fix this by moving the #endif to the right place. In addition the code
for Cygwin is made more robust: If a future Cygwin compiler defines
_GNU_SOURCE, too, the code will still work.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

training/pango_font_info.cpp

@@ -25,14 +25,14 @@
 #if (defined __MINGW32__) || (defined __CYGWIN__)
 // workaround for stdlib.h and putenv
 #undef __STRICT_ANSI__
-#endif
 
 #if (defined __MINGW32__)
 #include "strcasestr.h"
-#else
+#elif !defined(_GNU_SOURCE)
 // needed for strcasestr in string.h
 #define _GNU_SOURCE
 #endif
+#endif
 
 #include <stdlib.h>
 #include <stdio.h>