perf tools: Fix a clang 7.0 compilation error

Arnaldo reported the perf build failure with latest llvm/clang compiler
(7.0).

   $ make LIBCLANGLLVM=1 -C tools/perf/
   <SNIP>
    CC       /tmp/tmp.t53Qo38zci/tests/kmod-path.o
   util/c++/clang.cpp: In function ‘std::unique_ptr<llvm::SmallVectorImpl<char> >
       perf::getBPFObjectFromModule(llvm::Module*)’:
   util/c++/clang.cpp:150:43: error: no matching function for call to
       ‘llvm::TargetMachine::addPassesToEmitFile(llvm::legacy::PassManager&,
        llvm::raw_svector_ostream&, llvm::TargetMachine::CodeGenFileType)’
               TargetMachine::CGFT_ObjectFile)) {
                                             ^
   In file included from util/c++/clang.cpp:25:0:
   /usr/local/include/llvm/Target/TargetMachine.h:254:16: note: candidate:
       virtual bool llvm::TargetMachine::addPassesToEmitFile(
       llvm::legacy::PassManagerBase&, llvm::raw_pwrite_stream&,
       llvm::raw_pwrite_stream*, llvm::TargetMachine::CodeGenFileType, bool,
       llvm::MachineModuleInfo*)
     virtual bool addPassesToEmitFile(PassManagerBase &, raw_pwrite_stream &,
                  ^~~~~~~~~~~~~~~~~~~
  /usr/local/include/llvm/Target/TargetMachine.h:254:16: note:
      candidate expects 6 arguments, 3 provided
  mv: cannot stat '/tmp/tmp.t53Qo38zci/util/c++/.clang.o.tmp': No such file or directory
  make[7]: *** [/home/acme/git/perf/tools/build/Makefile.build:101:
      /tmp/tmp.t53Qo38zci/util/c++/clang.o] Error 1
  make[6]: *** [/home/acme/git/perf/tools/build/Makefile.build:139: c++] Error 2
  make[5]: *** [/home/acme/git/perf/tools/build/Makefile.build:139: util] Error 2
  make[5]: *** Waiting for unfinished jobs....
    CC       /tmp/tmp.t53Qo38zci/tests/thread-map.o

The function addPassesToEmitFile signature changed in llvm 7.0 and such
a change caused the failure. This patch fixed the issue with using
proper function signatures under different compiler versions.

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20180616174739.1076733-1-yhs@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/c++/clang.cpp

@@ -146,8 +146,15 @@ getBPFObjectFromModule(llvm::Module *Module)
 	raw_svector_ostream ostream(*Buffer);
 
 	legacy::PassManager PM;
-	if (TargetMachine->addPassesToEmitFile(PM, ostream,
-					       TargetMachine::CGFT_ObjectFile)) {
+	bool NotAdded;
+#if CLANG_VERSION_MAJOR < 7
+	NotAdded = TargetMachine->addPassesToEmitFile(PM, ostream,
+						      TargetMachine::CGFT_ObjectFile);
+#else
+	NotAdded = TargetMachine->addPassesToEmitFile(PM, ostream, nullptr,
+						      TargetMachine::CGFT_ObjectFile);
+#endif
+	if (NotAdded) {
 		llvm::errs() << "TargetMachine can't emit a file of this type\n";
 		return std::unique_ptr<llvm::SmallVectorImpl<char>>(nullptr);;
 	}