Committed: Fix for C99 thinko in c++/3394 fix (but still present on branch)

[Robert Lipe]

> You must not use C99 constructs in gcc (presumably for at least the
> next 10 years ;-) not even in non-C front-ends.  There

Since we allow GCC-specific extensions in non-C front ends and we
document that the only supported way to build the non-C front ends is
with 'make bootstrap', what's the distinction here?

> should be some option used to prevent this at build time, so
> you'd see a build error in a native bootstrap too.  I see the

IMO, the first few lines of every front end need to be a test to see if
the compiler being used is a GCC that's deemed "recent enough" and issue
a hard failure if not.  That the code builds at all with a "make" and
an arbitrary compiler has proven to be little more than an attractive
nuiscance over recent years.

RJL