Use the full path for kconf_update when running it

It is not on $PATH, so we cannot just expect QProcess to find it.

REVIEW: 117023

src/core/CMakeLists.txt

@@ -19,6 +19,11 @@ add_library(KF5ConfigCore ${libkconfigcore_SRCS})
 generate_export_header(KF5ConfigCore BASE_NAME KConfigCore)
 add_library(KF5::ConfigCore ALIAS KF5ConfigCore)
 
+target_compile_definitions(KF5ConfigCore
+    PRIVATE
+        KCONF_UPDATE_INSTALL_LOCATION="${CMAKE_INSTALL_PREFIX}/${LIBEXEC_INSTALL_DIR}/$<TARGET_FILE_NAME:KF5::kconf_update>"
+)
+
 target_include_directories(KF5ConfigCore INTERFACE "$<INSTALL_INTERFACE:${INCLUDE_INSTALL_DIR}/KConfigCore>")
 
 target_link_libraries(KF5ConfigCore PUBLIC Qt5::Core)

src/core/kconfig.cpp

@@ -483,7 +483,7 @@ void KConfig::checkUpdate(const QString &id, const QString &updateFile)
     const QString cfg_id = updateFile + QLatin1Char(':') + id;
     const QStringList ids = cg.readEntry("update_info", QStringList());
     if (!ids.contains(cfg_id)) {
-        QProcess::execute(QString::fromLatin1("kconf_update"), QStringList() << QString::fromLatin1("--check") << updateFile);
+        QProcess::execute(QStringLiteral(KCONF_UPDATE_INSTALL_LOCATION), QStringList() << QString::fromLatin1("--check") << updateFile);
         reparseConfiguration();
     }
 }