CMake build: Qt6 build fixes

Set Qt5_VERSION for version checks (e.g. currently still JavaScript
locator filter).

Export special FindQt5.cmake for external plugins and super-repo builds.

Change-Id: I5edb8b0e8bef1a341cd2ff04a13d0a6ce22f6558
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

cmake/FindQt5.cmake

@@ -51,6 +51,7 @@ foreach(comp IN LISTS Qt5_FIND_COMPONENTS)
 endforeach()
 
 set(Qt5_FOUND ${Qt6_FOUND})
+set(Qt5_VERSION ${Qt6_VERSION})
 
 foreach(tool qmake lrelease moc)
   if (TARGET Qt6::${tool} AND NOT TARGET Qt5::${tool})

src/CMakeLists.txt

@@ -35,8 +35,11 @@ install(EXPORT QtCreator
 )
 
 file(WRITE ${CMAKE_BINARY_DIR}/cmake/QtCreatorConfig.cmake "
+\# add module path for special FindQt5.cmake that considers Qt6 too
+list(APPEND CMAKE_MODULE_PATH \${CMAKE_CURRENT_LIST_DIR})
+
 include(CMakeFindDependencyMacro)
-find_dependency(Qt5
+find_dependency(Qt5 ${IDE_QT_VERSION_MIN}
   COMPONENTS Concurrent Core Network PrintSupport Qml Quick QuickWidgets Sql REQUIRED
 )
 
@@ -72,6 +75,7 @@ file(COPY
   ${PROJECT_SOURCE_DIR}/cmake/QtCreatorDocumentation.cmake
   ${PROJECT_SOURCE_DIR}/cmake/QtCreatorAPI.cmake
   ${PROJECT_SOURCE_DIR}/cmake/QtCreatorAPIInternal.cmake
+  ${PROJECT_SOURCE_DIR}/cmake/FindQt5.cmake
   DESTINATION ${CMAKE_BINARY_DIR}/cmake
 )