Clang: enable clang tidy and clazy in code model

Set QTC_CLANG_PLUGINS_LOAD env variable to get diagnostics
that come from libclang plugins.
This functionality works after the patch is applied to
clang repository and clang is properly built with it.

Task-number: QTCREATORBUG-15157
Change-Id: Iefeee4dd115f3f43ddc6ed79452a1135e653def6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

dist/clang/patches/README

@@ -37,3 +37,10 @@ QTCREATORBUG-15449_Fix-files-lock-on-Windows.patch
 
     Significantly reduces problems when saving a header file on Windows.
 
+QTCREATORBUG-15157_Link-with-clazy.patch
+
+    https://bugreports.qt.io/browse/QTCREATORBUG-15157
+
+    Introduces the flag CLANG_ENABLE_CLAZY to link libclang with Clazy and
+    forces link for Clazy checks and plugin registry entry.
+

src/plugins/clangcodemodel/clangutils.cpp

@@ -79,6 +79,12 @@ static QString creatorResourcePath()
 #endif
 }
 
+static bool loadClangPlugins()
+{
+    static bool load = qEnvironmentVariableIntValue("QTC_CLANG_PLUGINS_LOAD");
+    return load;
+}
+
 class LibClangOptionsBuilder final : public CompilerOptionsBuilder
 {
 public:
@@ -96,6 +102,10 @@ public:
     void addExtraOptions() final
     {
         addDummyUiHeaderOnDiskIncludePath();
+        if (loadClangPlugins()) {
+            addTidyPlugin();
+            addClazyPlugin();
+        }
         add("-fmessage-length=0");
         add("-fdiagnostics-show-note-include-stack");
         add("-fmacro-backtrace-limit=0");
@@ -123,6 +133,26 @@ private:
         if (!path.isEmpty())
             add(includeDirOption() + QDir::toNativeSeparators(path));
     }
+
+    void addClazyPlugin()
+    {
+        add("-Xclang");
+        add("-add-plugin");
+        add("-Xclang");
+        add("clang-lazy");
+    }
+
+    void addTidyPlugin()
+    {
+        add("-Xclang");
+        add("-add-plugin");
+        add("-Xclang");
+        add("clang-tidy");
+        add("-Xclang");
+        add("-plugin-arg-clang-tidy");
+        add("-Xclang");
+        add("-checks='-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,readability-identifier-naming'");
+    }
 };
 
 /**