Use the STL's make_unique if available
Use the STL's make_unique if available

Fixes build errors with GCC7.3.1 + LLVM5.0.1 under Centos.

/bcc/src/cc/frontends/b/loader.cc: In member function 'int ebpf::BLoader::parse(llvm::Module*, const string&, const string&, ebpf::TableStorage&, const string&, const string&)':
/bcc/src/cc/frontends/b/loader.cc:39:63: error: call of overloaded 'make_unique<ebpf::cc::Parser>(const string&)' is ambiguous
   proto_parser_ = make_unique<ebpf::cc::Parser>(proto_filename);
                                                               ^
In file included from /bcc/src/cc/frontends/b/node.h:26:0,
                 from /bcc/src/cc/frontends/b/parser.h:20,
                 from /bcc/src/cc/frontends/b/loader.cc:17:
/bcc/src/cc/common.h:28:1: note: candidate: typename std::enable_if<(! std::is_array< <template-parameter-1-1> >::value), std::unique_ptr<_Tp> >::type e/*
bpf::make_unique(Args&& ...) [with T = ebpf::cc::Parser; Args = {const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&}; typename std::enable_if<(! std::is_array< <template-parameter-1-1> >::value), std::unique_ptr<_Tp> >::type = std::unique_ptr<ebpf::cc::Parser>]
 make_unique(Args &&... args) {
 ^~~~~~~~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/memory:80:0,
                 from /bcc/src/cc/frontends/b/node.h:22,
                 from /bcc/src/cc/frontends/b/parser.h:20,
                 from /bcc/src/cc/frontends/b/loader.cc:17:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/unique_ptr.h:824:5: note: candidate: typename std::_MakeUniq<_Tp>::__single_object std::make_unique(_Args&& ...) [with _Tp = ebpf::cc::Parser; _Args = {const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&}; typename std::_MakeUniq<_Tp>::__single_object = std::unique_ptr<ebpf::cc::Parser>]
     make_unique(_Args&&... __args)
     ^~~~~~~~~~~

Signed-off-by: Kyle Zhang <3c25b01657254677d3e1a8fd1f0742c5d489bd39@smartx.com>

tuxology/bcc,brendangregg/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,tuxology/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,tuxology/bcc