[clang] Add getClangVendor() and use it in CodeGenModule.cpp (#75935)

In 9a38a72 `ProductId` was assigned from the stringified value of
`CLANG_VENDOR`, if that macro was defined. However, `CLANG_VENDOR` is
supposed to be a string, as it is defined (optionally) as such in the
top-level clang `CMakeLists.txt`.

Move the addition of `-DCLANG_VENDOR` to the compiler flags from
`clang/lib/Basic/CMakeLists.txt` to the top-level `CMakeLists.txt`, so
it is consistent across the whole clang codebase. Then remove the
stringification from `CodeGenModule.cpp`, to make it work correctly.

Fixes:		9a38a72

clang/include/clang/Basic/Version.h

@@ -40,6 +40,9 @@ namespace clang {
   /// string as getClangRevision.
   std::string getLLVMRevision();
 
+  /// Retrieves the Clang vendor tag.
+  std::string getClangVendor();
+
   /// Retrieves the full repository version that is an amalgamation of
   /// the information in getClangRepositoryPath() and getClangRevision().
   std::string getClangFullRepositoryVersion();

clang/lib/Basic/Version.cpp

@@ -57,6 +57,14 @@ std::string getLLVMRevision() {
 #endif
 }
 
+std::string getClangVendor() {
+#ifdef CLANG_VENDOR
+  return CLANG_VENDOR;
+#else
+  return "";
+#endif
+}
+
 std::string getClangFullRepositoryVersion() {
   std::string buf;
   llvm::raw_string_ostream OS(buf);
@@ -92,10 +100,7 @@ std::string getClangFullVersion() {
 std::string getClangToolFullVersion(StringRef ToolName) {
   std::string buf;
   llvm::raw_string_ostream OS(buf);
-#ifdef CLANG_VENDOR
-  OS << CLANG_VENDOR;
-#endif
-  OS << ToolName << " version " CLANG_VERSION_STRING;
+  OS << getClangVendor() << ToolName << " version " CLANG_VERSION_STRING;
 
   std::string repo = getClangFullRepositoryVersion();
   if (!repo.empty()) {
@@ -110,10 +115,7 @@ std::string getClangFullCPPVersion() {
   // the one we report on the command line.
   std::string buf;
   llvm::raw_string_ostream OS(buf);
-#ifdef CLANG_VENDOR
-  OS << CLANG_VENDOR;
-#endif
-  OS << "Clang " CLANG_VERSION_STRING;
+  OS << getClangVendor() << "Clang " CLANG_VERSION_STRING;
 
   std::string repo = getClangFullRepositoryVersion();
   if (!repo.empty()) {

clang/lib/CodeGen/CodeGenModule.cpp

@@ -995,12 +995,7 @@ void CodeGenModule::Release() {
                               uint32_t(CLANG_VERSION_MINOR));
     getModule().addModuleFlag(llvm::Module::Warning, "zos_product_patchlevel",
                               uint32_t(CLANG_VERSION_PATCHLEVEL));
-    std::string ProductId;
-#ifdef CLANG_VENDOR
-    ProductId = #CLANG_VENDOR;
-#else
-    ProductId = "clang";
-#endif
+    std::string ProductId = getClangVendor() + "clang";
     getModule().addModuleFlag(llvm::Module::Error, "zos_product_id",
                               llvm::MDString::get(VMContext, ProductId));