Clang: Emit a warning if LLVM_INSTALL_DIR is not set

Change-Id: I18f02e0878e2037857ccd85943c13bbac9cade6b
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>
Reviewed-by: hjk <hjk@theqtcompany.com>

qbs/modules/libclang/libclang.qbs

@@ -27,7 +27,10 @@ Module {
     property stringList llvmLibs: clangProbe.llvmLibs
 
     validate: {
-        if (!clangProbe.found)
+        if (!clangProbe.found) {
+            console.warn("Set LLVM_INSTALL_DIR to build the Clang Code Model."
+                         + " For details, see doc/src/editors/creator-clang-codemodel.qdoc.");
             throw "No usable libclang found";
+        }
     }
 }

src/plugins/plugins.pro

@@ -75,6 +75,9 @@ exists(../shared/qbs/qbs.pro)|!isEmpty(QBS_INSTALL_DIR): \
 isEmpty(LLVM_INSTALL_DIR):LLVM_INSTALL_DIR=$$(LLVM_INSTALL_DIR)
 exists($$LLVM_INSTALL_DIR) {
     SUBDIRS += clangcodemodel
+} else {
+    warning("Set LLVM_INSTALL_DIR to build the Clang Code Model. " \
+            "For details, see doc/src/editors/creator-clang-codemodel.qdoc.")
 }
 
 isEmpty(IDE_PACKAGE_MODE) {