build: make ABI_FILE workaround more prominent

Just to document this again: if we cross-build, /bin/sh may be a
native-xtool implementation with the wrong ELF ABI.  pkg(8) normally
looks up /bin/sh to figure out the ABI, but ABI_FILE is implemented
in libpkg to circumvent this.

build/common.sh

@@ -188,6 +188,7 @@ fi
 # misc. foo
 export CPUS=$(sysctl kern.smp.cpus | awk '{ print $2 }')
 export CONFIG_XML="/usr/local/etc/config.xml"
+export ABI_FILE="/usr/lib/crt1.o"
 export LABEL=${PRODUCT_NAME}
 export ENV_FILTER="env -i USER=${USER} LOGNAME=${LOGNAME} HOME=${HOME} \
 SHELL=${SHELL} BLOCKSIZE=${BLOCKSIZE} MAIL=${MAIL} PATH=${PATH} \

build/ports.sh

@@ -62,9 +62,6 @@ unset STAGEDIR
 # clobbers build for pkg(8) at least, since ARCH= is in there:
 unset MAKEFLAGS
 
-# Tell pkg(8) not to peek at /bin/sh
-export ABI_FILE=/usr/lib/crt1.o
-
 # Set up environment for target
 export TARGET_ARCH=${PRODUCT_ARCH}
 export TARGET=${PRODUCT_TARGET}