Build fails without USE_ORCJIT

[nalimilan]

Maybe that's expected, but when I remove #define USE_ORCJIT from src/llvm-version.h, the build fails with (in-tree) LLVM 3.7.1. This is annoying to debug performance regressions like #15246.

In file included from /home/milan/Dev/julia/src/codegen.cpp:24:0:
/home/milan/Dev/julia/usr/include/llvm/ExecutionEngine/ExecutionEngine.h: Dans la fonction ‘void* jl_get_global(llvm::GlobalVariable*)’:
/home/milan/Dev/julia/usr/include/llvm/ExecutionEngine/ExecutionEngine.h:156:15: erreur: ‘std::__cxx11::string llvm::ExecutionEngine::getMangledName(const llvm::GlobalValue*)’ is protected
   std::string getMangledName(const GlobalValue *GV);
               ^
In file included from /home/milan/Dev/julia/src/codegen.cpp:426:0:
/home/milan/Dev/julia/src/jitlayers.cpp:783:50: erreur: à l'intérieur du contexte
             jl_ExecutionEngine->getMangledName(gv));
                                                  ^
In file included from /home/milan/Dev/julia/src/codegen.cpp:24:0:
/home/milan/Dev/julia/usr/include/llvm/ExecutionEngine/ExecutionEngine.h: Dans la fonction ‘const jl_value_t* jl_dump_function_asm(void*, int)’:
/home/milan/Dev/julia/usr/include/llvm/ExecutionEngine/ExecutionEngine.h:156:15: erreur: ‘std::__cxx11::string llvm::ExecutionEngine::getMangledName(const llvm::GlobalValue*)’ is protected
   std::string getMangledName(const GlobalValue *GV);
               ^
/home/milan/Dev/julia/src/codegen.cpp:1389:53: erreur: à l'intérieur du contexte
             jl_ExecutionEngine->getMangledName(llvmf));
                                                     ^
Makefile:99: recipe for target 'codegen.o' failed
make[1]: *** [codegen.o] Error 1
make[1]: *** Attente des tâches non terminées....
Makefile:90: recipe for target 'julia-src-release' failed
make: *** [julia-src-release] Error 2