problem cross compiling with pkg-config (wrong port installed?)

[Fab Stz <fabstz-it@yahoo.fr>]

Dear mentors,

I'm trying to cross-build a package with host=arm64, arch=amd64.

In d/control I have:

Build-Depends: debhelper-compat (= 13), pkg-config

The problem, is compilation fails with error:
"Package *** was not found in the pkg-config search path."

dh_autobuild's command log says:

make -j2 "INSTALL=install --strip-program=true" PKG_CONFIG=aarch64-linux-gnu-
pkg-config CXX=aarch64-linux-gnu-g\+\+ CC=aarch64-linux-gnu-gcc

If I manually install only pkg-config:arm64, then it builds
If I manually install only pkg-config:amd64, then build fails.
Putting pkg-config:arm64 in the Build-depends works too (build succeeds)

Is dpkg installing the wrong pkg-config port?
What am I missing?

BTW: The package that pkg-config searches for is installed, I just don't 
mention it here in the build-deps for simplicity.

Rgds
Fab