qtsvg does not get built in out-of-tree Qt compile

I tried to build the Qt 5.15.0 branch from git, and also the 5.12.7 source from the commercial tarball.

I configured it to build in a directory outside the source tree. ie

mkdir build && cd build && ../qt5/configure ...

In both cases, it did not build qtsvg. It's in the makefile, but there is no qtsvg directory in the build tree after configure, so the makefile does nothing.

The module builds OK if built in-tree.