CMake: pro2cmake: Handle system tiff feature

Don't exclude it, because we use it in qtimageformats.

Change-Id: I0004830580dd9711cf7a5bd934ecd5a7f9036800
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Leander Beernaert <leander.beernaert@qt.io>

util/cmake/pro2cmake.py

@@ -1568,6 +1568,7 @@ def map_condition(condition: str) -> str:
                     and is_known_3rd_party_library(feature_name[7:])
                     and not feature_name.startswith("system_jpeg")
                     and not feature_name.startswith("system_zlib")
+                    and not feature_name.startswith("system_tiff")
                     and not feature_name.startswith("system_doubleconversion")
                 ):
                     part = "ON"