Using the following C compiler on alphaev6-dec-osf4.0f

% cc -V | head -1
DEC C V5.9-010 on Digital UNIX V4.0 (Rev. 1229)

GDB won't build (both CVS and mainline).  One of the reasons is that
expect contains an ill-formed C construct that the DEC C compiler
rejects (actually, it warns about it, but the #define fails to take
effect).  This patch fixes the problem.  I don't know whether this is
already fixed in expect upstream, so I'm Cc:ing Don Libes.

GDB/expect maintainers, ok to install in mainline and 5.2 branch?