gdb.fortran/lbound-ubound.exp: read expected lbound and ubound from function parameters (PR 30414)

gdb.fortran/lbound-ubound.exp reads the expected lbound and ubound
values by reading some output from the inferior.  This is racy when
running on boards where the inferior I/O is on a separate TTY than
GDB's, such as native-gdbserver.

I sometimes see this behavior:

    (gdb) continue
    Continuing.

    Breakpoint 2, do_test (lb=..., ub=...) at /home/jenkins/workspace/binutils-gdb_master_linuxbuild/platform/jammy-amd64/target_board/nati
    ve-gdbserver/src/binutils-gdb/gdb/testsuite/gdb.fortran/lbound-ubound.F90:45
    45        print *, ""   ! Test Breakpoint
    (gdb) Remote debugging from host ::1, port 37496

     Expected GDB Output:

    LBOUND = (-8, -10)
    UBOUND = (-1, -2)
    APB: Run a test here
    APB: Expected lbound '(-8, -10)'
    APB: Expected ubound ''

What happened is that expect read the output from GDB before the output
from the inferior, triggering this gdb_test_multiple clause:

    -re "$gdb_prompt $" {
        set found_prompt true

        if {$found_dealloc_breakpoint
            || ($expected_lbound != "" && $expected_ubound != "")} {
            # We're done.
        } else {
            exp_continue
        }
    }

So it set found_prompt, but the gdb_test_multiple kept going because
found_dealloc_breakpoint is false (this is the flag indicating that the
test is finished) and we still don't have expected_lbound and
expected_ubound.  Then, expect reads in the inferior I/O, triggering
this clause:

    -re ".*LBOUND = (\[^\r\n\]+)\r\n" {
        set expected_lbound $expect_out(1,string)
        if {!$found_prompt} {
            exp_continue
        }
    }

This sets expected_lbound, but since found_prompt is true, we don't do
exp_continue, and exit the gdb_test_multiple, without having an
expected_ubound.

Change the test to read the values from the lb and ub function
parameters instead.  As far as I understand, this still exercises what
we want to test.  These variables contain the return values of the
lbound and ubound functions as computed by the program.  We'll use them
to check the return values of the lbound and ubound functions as
computed by GDB.

Change-Id: I3c4d3d17d9291870a758a42301d15a007821ebb5
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30414