cobol: Fix up COBOL -include [PR119777]

cobol: Fix up COBOL -include [PR119777]

I was looking through options.cc diff between GCC 14 and 15, looking for
entries with added CL_Cobol where at least one other language is present
and was present before too.  Besides the -fsyntax-only changes this is
the only other one I found, COBOL adds Var(cobol_include) to something
which didn't have a Var at all before and IMHO it is actively harmful.
Because one can specify multiple -include file1 -include file2 options,
both in C/C++ etc. and in COBOL as well (as documented in the man
page).  A Var can track just one entry.  cobol_langhook_handle_option
should use arg instead.

2025-04-14  Jakub Jelinek  <jakub@redhat.com>

	PR cobol/119777
	* lang.opt (include): Remove Var(cobol_include).
	* cobol1.cc (cobol_langhook_handle_option) <case OPT_include>: Use
	arg instead of cobol_include.