-Dusethreads and -Duserelocatableinc are supposed to be arguments to Configure, not to gcc. So you want something like:

sh Configure -des -Dcc="gcc -m32" -Dusethreads -Duserelocatableinc -Dp
+refix=/usr/Thirdparty/perl/5.28.0/
[download]

Dave.