gdb/fortran: test case modified to suit the clang behavior.

As mentioned in the test case itself, depending on the fortran compiler
used, class member names used in the print commands and also output of
these print commands varies. Existing print commands and its output are
suited for gfortran, hence they were failing with clang compiler and test
case was modified accordingly for clang compiler.

gdb/testsuite/ChangeLog:
        * gdb.base/class-allocatable-array.exp: Modified test for clang.