[RFA]Use prev_lexptr in *-exp.y

[Michael Elizabeth Chastain]

> Michael, I think Pierre was talking about Modula 2, Java, 
> and Fortran.  Does your testing cover those?

There are no Modula 2 tests in the test suite, as far as I can see.
So I don't have any coverage for Modula 2.

I don't cover Java.  That is on my to-do list.

There are two scripts in gdb.fortran with 116 tests.  I cover those.
The tests are very basic; they don't actually compile any FORTRAN code.
They just exercise the expression parser.

Michael C