Re-implement the build_command() command to use "cmake --build" instead
of generating a native build tool invocation directly. This command
will internally invoke the proper native build tool.
This avoids requiring cmGlobalGenerator::GenerateBuildCommand to produce
a string so that it can be later refactored to produce a vector with no
quoting or escaping. It will also allow us to later teach CMake to
delay the decision about which build tool to invoke until after the
project build system is generated to disk. For example, on Visual
Studio 10 and above the preferred command-line tool is MSBuild, but we
need to fall back to devenv if the .sln has Intel Fortran .vfproj files.
If CMAKE_MAKE_PROGRAM is not set fail with an error message instead of
crashing. Suggest calling project() or enable_language() first to
ensure that CMAKE_MAKE_PROGRAM is set.
Brad King