pkg-config difference when run in pkgsrc vs normal run?

I have bunch of those line is Makefile:

LIBS += `pkg-config --libs OpenEXR 2>/dev/null`

this seems to work on Linux and when I directly run configure/gmake for package I am trying to create in pkgsrc-wip [cingg-netbsd]

But if I use pkgsrc for some reason this line gives empty output, so I resort to hacks like

https://github.com/NetBSD/pkgsrc-wip/blob/c94094925f2607a4982393d38f0eca99774c1cbc/cingg-netbsd/patches/patch-aa

Now, line for lv2 support will be even longer and apparently it does not work at configure stage, where I have also some calls to pkg-config in configure.ac :

if test "x$WANT_LV2" != "xno"; then GTK2_LIBS=`pkg-config --libs gtk+-2.0`

AC_CHECK_LIB([m], [gtk_init], [HAVE_gtk=yes], [HAVE_gtk=no], [$GTK2_LIBS])

test "x$HAVE_gtk" != "xno" && test -z "`pkg-config --cflags gtk+-2.0`" && HAVE_gtk=no

test "x$HAVE_gtk" != "xno" && test -z "`pkg-config --libs gtk+-2.0`" && HAVE_gtk=no

if test "x$HAVE_gtk" = "xno"; then

AC_MSG_ERROR([LV2 requires gtk+-2.0 support.])

Not sure why this happen, I tried to add pkg-config to USE_TOOLS variable in Makefile (no change), and checked that configure.ac sees pkg-config. May be PKG_CONFIG_PATH is not set when building inside pkgsrc system ?