Workaround for broken GCC

There appears to be broken GCC out there,
at least some "gcc (Debian 6.3.0-18) 6.3.0 20170516",
even with -std=gnu++17, reportedly does not treat
the in-class declaration of MAX_WIDTH as a definition,
and needs this old-style out-of-class definition, too.

See also bc2ae79f

Change-Id: Iaeb85e244d5963c01a86806f481c9d667b1f26a1
Reviewed-on: https://gerrit.libreoffice.org/49431Reviewed-by: Jim Raykowski <raykowj@gmail.com>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sw/source/filter/xml/xmltbli.cxx

@@ -1228,7 +1228,7 @@ public:
     }
 };
 
-#if __cplusplus <= 201402 || (defined __GNUC__ && __GNUC__ == 5 && __GNUC_MINOR__ <= 4)
+#if __cplusplus <= 201402 || (defined __GNUC__ && __GNUC__ <= 6)
 constexpr sal_Int32 SwXMLTableContext::MAX_WIDTH;
 #endif