FALLTHRUGH warning gcc-7

[cvvergara]

There is a: ​https://travis-ci.org/OSGeo/geos/jobs/331384379#L4304

FALLTHRUGH warning on g++11 when using gcc-7

home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:113:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
    input >>= 6;
    ~~~~~~^~~~~
/home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:114:3: note: here
   case 3:
   ^~~~
/home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:117:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
    input >>= 6;
    ~~~~~~^~~~~
/home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:118:3: note: here
   case 2:
   ^~~~
/home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:121:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
    input >>= 6;
    ~~~~~~^~~~~
/home/travis/build/OSGeo/geos/tests/xmltester/tinyxml/tinyxmlparser.cpp:122:3: note: here

[strk]

tinyxml is an external piece of code, I'd actually like to drop it and rely on system installed version (version 2 is packaged these days).

There is a tinyxml2 branch in git which was aimed at this, do you feel like bringing it up to date ?

[robe]

move this back if you plan to get to it before 3.7.0 release.

I suppose since it's just a testing tool it can go in beta or even rc.

[cvvergara]

This is already fixed in master:

​https://git.osgeo.org/gitea/geos/geos/commit/99aeda0ea2ae41a5870bbc777dd5a4822ab43d7b

​https://travis-ci.org/cvvergara/geos/jobs/392300418#L1309