Shorten the output of `clang-format --version`, include revision number.

Before:
  $ clang-format  --version
  LLVM (http://llvm.org/):
    LLVM version 3.5svn
    Optimized build with assertions.
    Built Jan  3 2014 (14:28:46).
    Default target: x86_64-apple-darwin13.0.0
    Host CPU: core-avx-i

Now:
  $ bin/clang-format --version
  clang-format version 3.5 (198452)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198694 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/Version.h

@@ -70,6 +70,9 @@ namespace clang {
   /// and the vendor tag.
   std::string getClangFullVersion();
 
+  /// \brief Like getClangFullVersion(), but with a custom tool name.
+  std::string getClangToolFullVersion(llvm::StringRef ToolName);
+
   /// \brief Retrieves a string representing the complete clang version suitable
   /// for use in the CPP __VERSION__ macro, which includes the clang version
   /// number, the repository version, and the vendor tag.

lib/Basic/Version.cpp

@@ -116,12 +116,16 @@ std::string getClangFullRepositoryVersion() {
 }
 
 std::string getClangFullVersion() {
+  return getClangToolFullVersion("clang");
+}
+
+std::string getClangToolFullVersion(StringRef ToolName) {
   std::string buf;
   llvm::raw_string_ostream OS(buf);
 #ifdef CLANG_VENDOR
   OS << CLANG_VENDOR;
 #endif
-  OS << "clang version " CLANG_VERSION_STRING " "
+  OS << ToolName << " version " CLANG_VERSION_STRING " "
      << getClangFullRepositoryVersion();
 
   // If vendor supplied, include the base LLVM version as well.

tools/clang-format/ClangFormat.cpp

@@ -17,6 +17,7 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/Version.h"
 #include "clang/Format/Format.h"
 #include "clang/Lex/Lexer.h"
 #include "clang/Rewrite/Core/Rewriter.h"
@@ -255,6 +256,11 @@ static bool format(StringRef FileName) {
 }  // namespace format
 }  // namespace clang
 
+static void PrintVersion() {
+  raw_ostream &OS = outs();
+  OS << clang::getClangToolFullVersion("clang-format") << '\n';
+}
+
 int main(int argc, const char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal();
 
@@ -268,6 +274,7 @@ int main(int argc, const char **argv) {
       I->second->setHiddenFlag(cl::ReallyHidden);
   }
 
+  cl::SetVersionPrinter(PrintVersion);
   cl::ParseCommandLineOptions(
       argc, argv,
       "A tool to format C/C++/Obj-C code.\n\n"