The Sun compiler does not provide the proper vector constructor to
initialize it from an iterator pair of a non-matching type. Extend the
ParseUnixCommandLine API to provide a vector of the proper type so no
conversion is needed.
Many compilers we support do not provide the at() member of std::map.
Use the workaround added by commit a7e7a04a (Fix run_compile_commands
build on Apple GCC 3.3, 2011-05-16) for all compilers.