There's nothing about invoking build tools that precludes concurrent builds or which requires ad hoc shell scripts (although "unmaintainable scripts" is an iron

There's nothing about invoking build tools that precludes concurrent builds or which requires ad hoc shell scripts (although "unmaintainable scripts" is an ironic defense of CMake, since it's subject to all the same criticisms). Alternate solutions include Docker, Nix, or even plain makefiles depending on what your artifact needs to be. Posix is unrelated to invoking multiple build tools and assembling their results.