Similar to build_headermap(), but builds a dictionary of includes from
    the "source" files (i.e. ".c/.cc" files).

def build_sourcemap(sources):
    """
    Similar to build_headermap(), but builds a dictionary of includes from
    the "source" files (i.e. ".c/.cc" files).
    """
    sourcemap = {}
    for sfile in sources:
        inc = find_includes(sfile)
        sourcemap[sfile] = set(inc)
    return sourcemap