mit-scheme fails to cross build from source as it uses the build
architecture pkg-config (hard coded via the relevant configure.ac) to
locate the PostgreSQL library. I'm attaching a patch to make it use the
correct pkg-config.

Note that this does not fully fix the build. In the end, I am faced with
an illegal instruction. Please consider that out of scope for this
report and close it when just addressing the pkg-config usage.

Helmut