PKG_CONFIG_PATH variable has no effect under OS X

[wizard29]

Recently I downloaded IM 7.0.2-2.
It was surprise for me when "configure" script was finished and I didn't see usual delegates like PNG, JPEG, TIFF.
Usually, delegate libraries are installed to a custom folder. I use PKG_CONFIG_PATH variable to point to the delegate *.pc files.
I don't use ports for IM building under OS X because it brings a lot of deployment problems.

I don't understand what happens, it looks like a bug. Could anyone help me?

Environment: OS X 10.11.5, Xcode (LLVM)

[wizard29]

I did an experiment.
1. Untar IM 6.9.3-2
2. Untar delegate libraries which I want (zlib, lcms, openexr, xml, jpeg, png, tiff) to the IM 6.9.3-2 root folder.
3. Build delegates.
4. Install delegates to a custom folder like $HOME/3rdlibs/libs
5. Execute ./configure CXXFLAGS="-std=c++11 -mmacosx-version-min=10.11" CFLAGS="-O2 -mmacosx-version-min=10.11" CC="clang" CXX="clang++" LDFLAGS="-headerpad_max_install_names -mmacosx-version-min=10.11" --enable-hdri --enable-delegate-build --enable-shared --disable-installed --disable-static --disable-docs -with-quantum-depth=8 PKG_CONFIG_PATH=$HOME/3rdlibs/libs/lib/pkgconfig

As result I saw "DELEGATES = bzlib mpeg jng jpeg lcms openexr png tiff xml zlib" as I expected. But it doesn't work for IM 6.9.3-7 and above.