perf tools: LIBCLANGLLVM=1 build broken with llvm 7/clang 6

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Hi Wang, Yogong,

	While reviewing the BTF patches for pahole, I updated llvm/clang
to HEAD and then building perf with clang embedded I noticed this, will
investigate, posting here to document the regression, maybe this is
something you came across in other scenario:

 $ 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

- Arnaldo