[llvm-rc] Look for "clang-<major>" when locating a suitable preprocessor

[mstorsjo]

Summary

In some cases, there's no adjacent executable named "clang" or
"clang-cl", but one name "clang-<major>". This logic doesn't
cover every possible deployment setup of course, but should
cover more fairly common/reasonable cases.

See
https://github.com/curl/curl-for-win/commit/caaae171ac43af5b883403714dafd42030d8de61#commitcomment-105808524
for discussion about a case where this would have been helpful.

[aganea]

LG.

[mstorsjo]

Reordered the checks to check for "clang-<major>" before plain "clang", as suggested in the linked discussion.

llvm/tools/llvm-rc/llvm-rc.cpp

 //===----------------------------------------------------------------------===//
 
 #include "ResourceFileWriter.h"
 #include "ResourceScriptCppFilter.h"
 #include "ResourceScriptParser.h"
 #include "ResourceScriptStmt.h"
 #include "ResourceScriptToken.h"
 
+#include "llvm/Config/llvm-config.h"
 #include "llvm/Object/WindowsResource.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/InitLLVM.h"
if ((EC = sys::fs::createTemporaryFile(Prefix, Suffix, FileName)))
     fatalError("Unable to create temp file: " + EC.message());
   return static_cast<std::string>(FileName);
 }
 
 ErrorOr<std::string> findClang(const char *Argv0, StringRef Triple) {
   StringRef Parent = llvm::sys::path::parent_path(Argv0);
   ErrorOr<std::string> Path = std::error_code();
   std::string TargetClang = (Triple + "-clang").str();
+  std::string VersionedClang = ("clang-" + Twine(LLVM_VERSION_MAJOR)).str();
   if (!Parent.empty()) {
     // First look for the tool with all potential names in the specific
     // directory of Argv0, if known
-    for (const auto *Name : {TargetClang.c_str(), "clang", "clang-cl"}) {
+    for (const auto *Name :
+         {TargetClang.c_str(), VersionedClang.c_str(), "clang", "clang-cl"}) {
       Path = sys::findProgramByName(Name, Parent);
       if (Path)
         return Path;
     }
   }
   // If no parent directory known, or not found there, look everywhere in PATH
   for (const auto *Name : {"clang", "clang-cl"}) {
     Path = sys::findProgramByName(Name);