Dwarf: Fortran, support DW_TAG_entry_point.

Fortran provides additional entry-points to an subprogram.
Those entry-points may have only a subset of parameters
of the original subprogram as well.
Add support for parsing DW_TAG_entry_point's for Fortran.

2016-06-01  Bernhard Heckel  <bernhard.heckel@intel.com>

gdb/Changelog:
	* gdb/dwarf2read.c (add_partial_symbol): Handle DW_TAG_entry_point.
	(add_partial_entry_point): New.
	(add_partial_subprogram): Search for entry_points.
	(process_die): Handle DW_TAG_entry_point.
	(dwarf2_get_pc_bounds): Update low pc from DWARF.
	(load_partial_dies): Save DW_TAG_entry_point's.
	(load_partial_dies): Save DW_TAG_entry_point to hash table.
	(load_partial_dies): Look into child's of DW_TAG_sub_program
	for fortran.
	(new_symbol_full): Process DW_TAG_entry_point.
	(read_type_die_1): Handle DW_TAG_entry_point.

gdb/Testsuite/Changelog:
	* gdb.fortran/entry_point.f90: New.
	* gdb.fortran/entry_point.exp: New.

Change-Id: I886699802fc940cd9b995806c32a85a05cf57dc4