clang: Support user-provided llvm-config

... in the qmake and qbs builds. (The look-up mechanism in the cmake
build is completely different.)

Fixes: QTCREATORBUG-20592
Change-Id: I049740795108060aeada62dd030e82390e07fe48
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

qbs/modules/libclang/functions.js

@@ -35,6 +35,9 @@ function isSuitableLLVMConfig(llvmConfigCandidate, qtcFunctions)
 
 function llvmConfig(hostOS, qtcFunctions)
 {
+    var llvmConfigFromEnv = Environment.getEnv("LLVM_CONFIG");
+    if (llvmConfigFromEnv)
+        return llvmConfigFromEnv;
     var llvmInstallDirFromEnv = Environment.getEnv("LLVM_INSTALL_DIR")
     var llvmConfigVariants = [
         // CLANG-UPGRADE-CHECK: Adapt once we require a new minimum version.

qbs/modules/libclang/libclang.qbs

@@ -69,7 +69,7 @@ Module {
     validate: {
         if (!clangProbe.found) {
             console.warn("No usable libclang version found."
-                         + " Set LLVM_INSTALL_DIR to build the Clang Code Model."
+                         + " Set LLVM_CONFIG to build the Clang Code Model."
                          + " For details, see"
                          + " doc/src/editors/creator-only/creator-clang-codemodel.qdoc.");
             throw new Error();

src/shared/clang/clang_installation.pri

@@ -1,16 +1,21 @@
-isEmpty(LLVM_INSTALL_DIR):LLVM_INSTALL_DIR=$$(LLVM_INSTALL_DIR)
+isEmpty(LLVM_CONFIG): LLVM_CONFIG=$$(LLVM_CONFIG)
-LLVM_INSTALL_DIR = $$clean_path($$LLVM_INSTALL_DIR)
+llvm_config = $$clean_path($$LLVM_CONFIG)
+!isEmpty(llvm_config):!exists($$llvm_config) {
+    error("Explicitly given LLVM_CONFIG does not exist: $$llvm_config")
+}
 
-!isEmpty(LLVM_INSTALL_DIR):!exists($$LLVM_INSTALL_DIR) {
+isEmpty(LLVM_CONFIG) {
+    isEmpty(LLVM_INSTALL_DIR):LLVM_INSTALL_DIR=$$(LLVM_INSTALL_DIR)
+    LLVM_INSTALL_DIR = $$clean_path($$LLVM_INSTALL_DIR)
+    !isEmpty(LLVM_INSTALL_DIR):!exists($$LLVM_INSTALL_DIR) {
         error("Explicitly given LLVM_INSTALL_DIR does not exist: $$LLVM_INSTALL_DIR")
+    }
 }
 
 defineReplace(llvmWarningOrError) {
     warningText = $$1
-    errorText = $$2
+    isEmpty(llvm_config): warning($$warningText)
-    isEmpty(errorText): errorText = $$warningText
+    else: error($$warningText)
-    isEmpty(LLVM_INSTALL_DIR): warning($$warningText)
-    else: error($$errorText)
     return(false)
 }
 
@@ -134,29 +139,25 @@ defineReplace(extractWarnings) {
 BIN_EXTENSION =
 win32: BIN_EXTENSION = .exe
 
-isEmpty(LLVM_INSTALL_DIR) {
+isEmpty(llvm_config) {
-    unix {
+    isEmpty(LLVM_INSTALL_DIR) {
-        llvm_config = $$system(which llvm-config-11)
+        unix: llvm_config = $$system(which llvm-config-11)
-        isEmpty(llvm_config): llvm_config = $$system(which llvm-config-10)
-        isEmpty(llvm_config): llvm_config = $$system(which llvm-config-9)
-    }
         isEmpty(llvm_config): llvm_config = llvm-config
-} else {
+    } else {
         exists($$LLVM_INSTALL_DIR/bin/llvm-config-11$$BIN_EXTENSION) {
           llvm_config = $$system_quote($$LLVM_INSTALL_DIR/bin/llvm-config-11)
         } else {
           llvm_config = $$system_quote($$LLVM_INSTALL_DIR/bin/llvm-config)
           requires(exists($$llvm_config$$BIN_EXTENSION))
         }
+    }
 }
 
 output = $$system($$llvm_config --version, lines)
 LLVM_VERSION = $$extractVersion($$output)
 
 isEmpty(LLVM_VERSION) {
-    $$llvmWarningOrError(\
+    $$llvmWarningOrError("Cannot determine clang version. Set LLVM_CONFIG to build the Clang Code Model")
-        "Cannot determine clang version. Set LLVM_INSTALL_DIR to build the Clang Code Model",\
-        "LLVM_INSTALL_DIR does not contain a valid llvm-config, candidate: $$llvm_config")
 } else:!versionIsAtLeast($$LLVM_VERSION, 9, 0, 0): {
     # CLANG-UPGRADE-CHECK: Adapt minimum version numbers.
     $$llvmWarningOrError(\