writemain() takes an argument list of directories containing archive libraries
that relate to perl modules and should be linked into a new perl binary. It
writes a corresponding perlmain.c file that is a plain C file containing all
the bootstrap code to make the If the first argument to writemain() is a
reference to a scalar it is used as the file name to open for output. Any other
reference is used as the file handle to write to. Otherwise output defaults to
STDOUT.
