configure: Move QDoc clang versions into module

Previously, QDoc’s minimum and explicitly supported Clang versions were
defined in `.cmake.conf`, mixing tool-specific policy with repo-global
settings. These values also lived far from the QDoc configure logic and
messages that consume them.

This made updates easy to miss during QDoc changes and forced edits to
the top-level file for QDoc-only adjustments, adding noise to reviews.

This change introduces `src/qdoc/cmake/QDocConfiguration.cmake` and
moves QDOC_MINIMUM_CLANG_VERSION and QDOC_SUPPORTED_CLANG_VERSIONS
there. `configure.cmake` now includes this module alongside
`QDocConfigureMessages.cmake`, and the top-level definitions are
removed.

Behavior is unchanged. The configuration is now localized with the rest
of QDoc’s CMake logic, improving discoverability and making future edits
safer.

Task-number: QTBUG-137569
Pick-to: 6.8
Change-Id: I3ff0f8f1a9f19064b039c860adf6cae2e94aed47
Reviewed-by: Joerg Bornemann <[email protected]>
(cherry picked from commit 2bf4226)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
(cherry picked from commit 91c40ac)

Author: paulwicking

.cmake.conf

@@ -1,9 +1,5 @@
 set(QT_REPO_MODULE_VERSION "6.9.3")
 set(QT_REPO_MODULE_PRERELEASE_VERSION_SEGMENT "alpha1")
 set(QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_NO_AS_CONST=1")
-set(QDOC_MINIMUM_CLANG_VERSION "17")
-set(QDOC_SUPPORTED_CLANG_VERSIONS
-    "20.1" "19.1" "18.1" "17.0"
-)
 list(APPEND QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_NO_FOREACH=1")
 list(APPEND QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_NO_CONTEXTLESS_CONNECT=1")

configure.cmake

@@ -1,6 +1,9 @@
 # Copyright (C) 2022 The Qt Company Ltd.
 # SPDX-License-Identifier: BSD-3-Clause
 
+# Include QDoc-specific configuration early (needed for feature definitions)
+include(${CMAKE_CURRENT_LIST_DIR}/src/qdoc/cmake/QDocConfiguration.cmake)
+
 #### Tests
 
 qt_find_package(WrapLibClang 8 PROVIDED_TARGETS WrapLibClang::WrapLibClang)

src/qdoc/cmake/QDocConfiguration.cmake

@@ -0,0 +1,13 @@
+# Copyright (C) 2025 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+# QDoc-specific configuration variables
+
+# Minimum supported Clang version for QDoc
+set(QDOC_MINIMUM_CLANG_VERSION "17")
+
+# List of explicitly supported Clang versions for QDoc
+set(QDOC_SUPPORTED_CLANG_VERSIONS
+    "20.1" "19.1" "18.1" "17.0"
+)
+