Apparent error in gcc using -ansi option.

[wrb]

My environment: RH6.2 Linux, working with code ported from SCO.
I have noticed that when using the -ansi option, the sys/types.h
file is not able to process a section of code bounded by

#ifdef  __USE_BSD

which code contains a typedef for u_short.  If the -ansi option
is not used, the code is processed properly.  When using the 
options -ansi -E -dM, pipe to grep to search for USE_BSD, the
name __USE_BSD does not show up.  When -E -dM without the -ansi
option, the name __USE_BSD does show up.

Is there some ANSI justification by which the given name is
not legal, or is the observed behavior erroneous?  Should you
like, I will be happy to construct a simple example source code
file and a list of steps by which to demonstrate this behavior.

William R. Buckley