What bison versions are installed on buildfarm machines?

Is there any way to find out $subject?  I see that several of the
buildfarm machines are choking on a patch I committed yesterday:

guc-file.l: In function `ProcessConfigFile':
guc-file.l:162: error: `YY_FLUSH_BUFFER' undeclared (first use in this function)
guc-file.l:162: error: (Each undeclared identifier is reported only once
guc-file.l:162: error: for each function it appears in.)
make[4]: *** [guc.o] Error 1

YY_FLUSH_BUFFER is documented as a standard macro in bison 1.875, which
is the oldest version we officially support.  But I'm prepared to change
it if there is another way that would work with a wider range of bison
versions.
        regards, tom lane