Run time link error when using --coverage + clang + osx

[springmeyer]

We hit this error (Symbol not found: _llvm_gcda_emit_arcs) when building osrm-backend and node-osrm on OS X with clang and the --coverage flag. This does not manifest when only node-osrm is built with --coverage

module.js:356
  Module._extensions[extension](this, filename);
                               ^
Error: dlopen(/Users/travis/build/Project-OSRM/node-osrm/lib/binding/osrm.node, 1): Symbol not found: _llvm_gcda_emit_arcs

and -flto builds are hitting: lto1: internal compiler error: in add_symbol_to_partition_1, at lto/lto-partition.c:186

[springmeyer]

Closing:

• The Symbol not found: _llvm_gcda_emit_arcs error on OSX + clang + debug is gone now (likely a clang++ bug). No sign of it now with Apple LLVM version 7.0.0 (clang-700.1.76)
• The Linux -flto error lto1: internal compiler error: in add_symbol_to_partition_1 was a gcc 4.8 bug worked around in Project-OSRM/osrm-backend@119fb63 which allowed the removal of daa162b