gdb/fortran: add symbol base comparison operators

gdb/fortran: add symbol base comparison operators

Fortran supports symbol based comparison operators as well as the
classic text based comparison operators, so we have:

   Text     | Symbol
   Operator | Operator
   ---------|---------
   .eq.     | ==
   .ne.     | /=
   .le.     | <=
   .ge.     | >=
   .gt.     | >
   .lt.     | <

This commit adds the symbol based operators as well as some tests.

gdb/ChangeLog:

	* f-exp.y (dot_ops): Rename to...
	(fortran_operators): ...this.  Add a header comment.  Add symbol
	based operators.
	(yylex): Update to use fortran_operators not dot_ops.  Remove
	special handling for '**', this is now included in
	fortran_operators.

gdb/testsuite/ChangeLog:

	* gdb.fortran/dot-ops.exp: Add new tests.