package/icu: clear TARGET env variable

If the TARGET env variable is set icu may try to use it.

To prevent this from causing issues clear it from the icu env.

Fixes:
>>> host-icu 70-1 Building
PATH="/home/buildroot/buildroot/output/per-package/host-icu/host/bin:/home/buildroot/buildroot/output/per-package/host-icu/host/sbin:/home/buildroot/bin:/home/buildroot/.local/bin:/home/buildroot/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
PKG_CONFIG="/home/buildroot/buildroot/output/per-package/host-icu/host/bin/pkg-config"
PKG_CONFIG_SYSROOT_DIR="/" PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1
PKG_CONFIG_ALLOW_SYSTEM_LIBS=1
PKG_CONFIG_LIBDIR="/home/buildroot/buildroot/output/per-package/host-icu/host/lib/pkgconfig:/home/buildroot/buildroot/output/per-package/host-icu/host/share/pkgconfig"
 /usr/bin/make -j33  -C
/home/buildroot/buildroot/output/build/host-icu-70-1/source
cd ./config; \
    /usr/bin/make -f pkgdataMakefile
rm -rf config/icu-config
rebuilding config/icucross.mk
rebuilding config/icucross.inc
/bin/bash ./mkinstalldirs lib
/bin/bash ./mkinstalldirs bin
/usr/bin/install -c ./config/icu-config-top config/icu-config
rm -rf pkgdata.inc
chmod u+w config/icu-config
mkdir lib
mkdir bin
LC_ALL=C /usr/bin/sed -f ./config/make2sh.sed < ./config/Makefile.inc
| grep -v '#M#' | uniq >> config/icu-config
config/icu-uc.pc updated.
config/icu-i18n.pc updated.
/usr/bin/make[2]: Making `all' in `stubdata'
LC_ALL=C /usr/bin/sed -f ./config/make2sh.sed < ./config/mh-linux |
grep -v '#M#' | uniq >> config/icu-config
cat ./config/icu-config-bottom >> config/icu-config
   (deps)     stubdata.cpp
chmod u-w config/icu-config
Note: rebuild with "/usr/bin/make VERBOSE=1 " to show all compiler parameters.
make[3]: *** No rule to make target 'bpf', needed by 'all-local'.  Stop.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 17b6372790c33fa317ab6134ad6d5b8882b9cedd)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/icu/icu.mk

@@ -28,6 +28,13 @@ ICU_CONF_OPTS = \
 	--disable-samples \
 	--disable-tests
 
+# the icu build process breaks if the TARGET environment variable is
+# non-empty
+ICU_CONF_ENV += TARGET=""
+ICU_MAKE_ENV += TARGET=""
+HOST_ICU_CONF_ENV += TARGET=""
+HOST_ICU_MAKE_ENV += TARGET=""
+
 # When available, icu prefers to use C++11 atomics, which rely on the
 # __atomic builtins. On certain architectures, this requires linking
 # with libatomic starting from gcc 4.8.