Include QtPlatformSupport as part of find_package(Qt6BuildInternals)

This is needed because the ported over requires() clauses from qmake
to CMake are executed before qt_repo_build(), which means that all the
custom platform variables that we set (like LINUX, APPLE_OSX) need
to be available immediately after finding BuildInternals.

Change-Id: I7345b69edf72c266508846766e64f42c99862d1d
Reviewed-by: Qt CMake Build Bot
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

CMakeLists.txt

@@ -18,12 +18,13 @@ list(PREPEND CMAKE_MODULE_PATH
 )
 
 ## Find the build internals package.
+set(QT_BUILD_INTERNALS_SKIP_CMAKE_MODULE_PATH_ADDITION TRUE)
 list(PREPEND CMAKE_PREFIX_PATH
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
 )
 find_package(QtBuildInternals CMAKE_FIND_ROOT_PATH_BOTH)
-
-qt_build_repo_begin(SKIP_CMAKE_MODULE_PATH_ADDITION)
+unset(QT_BUILD_INTERNALS_SKIP_CMAKE_MODULE_PATH_ADDITION)
+qt_build_repo_begin()
 
 ## QtBase specific configure tests:
 include(QtBaseConfigureTests)

cmake/QtBuildInternals/QtBuildInternalsConfig.cmake

@@ -13,7 +13,7 @@ if(EXISTS "${CMAKE_CURRENT_LIST_DIR}/QtBuildInternalsExtra.cmake")
 endif()
 
 macro(qt_set_up_build_internals_paths)
-    # Set up the paths for the cmake modules located in the build dir. Prepend, so the paths are
+    # Set up the paths for the cmake modules located in the prefix dir. Prepend, so the paths are
     # least important compared to the source dir ones, but more important than command line
     # provided ones.
     set(QT_CMAKE_MODULE_PATH "${QT_BUILD_INTERNALS_PATH}/../${QT_CMAKE_EXPORT_NAMESPACE}")
@@ -39,13 +39,17 @@ macro(qt_set_up_build_internals_paths)
     endif()
 endmacro()
 
-macro(qt_build_repo_begin)
-    if(${ARGC} EQUAL 1 AND "${ARGV0}" STREQUAL "SKIP_CMAKE_MODULE_PATH_ADDITION")
-        # No-op.
-    else()
+# Set up the build internal paths unless explicitly requested not to.
+if(NOT QT_BUILD_INTERNALS_SKIP_CMAKE_MODULE_PATH_ADDITION)
     qt_set_up_build_internals_paths()
-    endif()
+endif()
 
+# Define some constants to check for certain platforms, etc.
+# Needs to be loaded before qt_repo_build() to handle require() clauses before even starting a repo
+# build.
+include(QtPlatformSupport)
+
+macro(qt_build_repo_begin)
     # Qt specific setup common for all modules:
     include(QtSetup)
     include(FeatureSummary)

cmake/QtSetup.cmake

@@ -90,9 +90,6 @@ enable_testing()
 # Set up building of examples.
 option(BUILD_EXAMPLES "Build Qt examples" ON)
 
-## Define some constants to check for certain platforms, etc:
-include(QtPlatformSupport)
-
 ## Android platform settings
 if(ANDROID)
     include(QtPlatformAndroid)