From this comment:

 *        d_Gconvert='gconvert((x),(n),(t),(b))'
 *        d_Gconvert='gcvt((x),(n),(b))'
 *        d_Gconvert='sprintf((b),"%.*g",(n),(x))'
[download]

... I assume that you should be able to influence the value of the Gconvert macro by supplying a value on the ./Configure command line:

sh ./Configure -des -DGconvert='sprintf(...)'
[download]

(but I have not tested this, nor do I really know how to determine if what I see is correct ;) )

The "real fix", I guess, would be to extend the Configure unit for Gconvert (likely d_gconvert.U) to check the output of the respective C programs and then choose an appropriate value...

Update: See below for Tux approach of setting up a Policy.sh file, to evade quoting problems etc