gdb: add compunit_symtab::set_primary_filetab method

Add a method to set the primary filetab of the CU.  This is currently
done in buildsym_compunit::end_symtab_with_blockvector.

Change-Id: I16c51a6b90a4cb4c0c5f183b0f2e12bc64b6fd74
3 files changed