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

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
curl/curl-for-win@caaae17#commitcomment-105808524
for discussion about a case where this would have been helpful.

Differential Revision: https://reviews.llvm.org/D146794

(cherry picked from commit 282744a)

Author: mstorsjo

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

@@ -18,6 +18,7 @@
 #include "ResourceScriptToken.h"
 
 #include "llvm/ADT/Triple.h"
+#include "llvm/Config/llvm-config.h"
 #include "llvm/Object/WindowsResource.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
@@ -137,10 +138,12 @@ 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;