[virtual provider] Add SQLITE3_INCLUDE_DIR to CMakeLists.txt

The virtual provider depends directly on sqlite3.h, but fails to add
explictly its paths, relying on it to be present in the other used
included paths, which may be not always the case in some setups.

src/providers/virtual/CMakeLists.txt

@@ -35,6 +35,7 @@ INCLUDE_DIRECTORIES(
 )
 INCLUDE_DIRECTORIES(SYSTEM
   ${POSTGRES_INCLUDE_DIR}
+  ${SQLITE3_INCLUDE_DIR}
   ${SPATIALITE_INCLUDE_DIR}
   ${GEOS_INCLUDE_DIR}
   ${QSCINTILLA_INCLUDE_DIR}