[patch,fortran] Fix keyword check for specifiers (PR29452)

[Tobias Burnus]

Hi,

FX Coudert wrote:
> OK for the revised version. I think it should go into 4.2 too; can you
> regtest it and commit it there also?
Regtested with x86_64-unknown-linux-gnu on the gcc-4_2-branch
and committed to trunk and gcc-4_2-branch.

Tobias