llvm::FindExecutable(): Retrieve the name with suffix.exe, if available.

bugpoint uses it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112803 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/SystemUtils.cpp b/lib/Support/SystemUtils.cpp
index 299032f..421b381 100644
--- a/lib/Support/SystemUtils.cpp
+++ b/lib/Support/SystemUtils.cpp
@@ -49,6 +49,10 @@
     Result.appendComponent(ExeName);
     if (Result.canExecute())
       return Result;
+    // Expect to retrieve the pathname with suffix .exe.
+    Result = sys::Program::FindProgramByName(Result.str());
+    if (!Result.empty())
+      return Result;
   }
 
   return sys::Path();