gdb/fortran: Add builtin 8-byte integer type with (kind=8) support

gdb/fortran: Add builtin 8-byte integer type with (kind=8) support

Add a new builtin type, an 8-byte integer, and allow GDB to parse
'integer (kind=8)', returning the new 8-byte integer.

gdb/ChangeLog:

	* f-exp.y (convert_to_kind_type): Handle integer (kind=8).
	* f-lang.c (build_fortran_types): Setup builtin_integer_s8.
	* f-lang.h (struct builtin_f_type): Add builtin_integer_s8 field.

gdb/testsuite/ChangeLog:

	* gdb.fortran/type-kinds.exp: Test new integer type kind.