[gdb/fortran] Fix literal truncation

As mentioned in commit 5b758627a18 ("Make gdb.base/parse_number.exp test all
architectures"):
...
    There might be a bug that 32-bit fortran truncates 64-bit values to
    32-bit, given "p/x 0xffffffffffffffff" returns "0xffffffff".
...

More concretely, we have:
...
$ for arch in i386:x86-64 i386; do \
    gdb -q -batch -ex "set arch $arch" -ex "set lang fortran" \
      -ex "p /x 0xffffffffffffffff"; \
  done
The target architecture is set to "i386:x86-64".
$1 = 0xffffffffffffffff
The target architecture is set to "i386".
$1 = 0xffffffff
...

Fix this by adding a range check in parse_number in gdb/f-exp.y.

Furthermore, make sure we error out on overflow instead of truncating in all
other cases.

Tested on x86_64-linux.