package/python-pyicu: fix build

Fixes:
http://autobuild.buildroot.net/results/977/977c043615603dd3541e23b81c5f11374606aff6/

Set environment variables to cross-compile friendly values, this prevents
icu-config picking up host libraries:
https://gitlab.pyicu.org/main/pyicu/-/blob/main/setup.py#L89
https://gitlab.pyicu.org/main/pyicu/-/blob/main/setup.py#L179
https://gitlab.pyicu.org/main/pyicu/-/blob/main/setup.py#L216

This follows the upstream build docs:
https://gitlab.pyicu.org/main/pyicu#building-pyicu

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

package/python-pyicu/python-pyicu.mk

@@ -12,4 +12,10 @@ PYTHON_PYICU_LICENSE_FILES = LICENSE
 PYTHON_PYICU_DEPENDENCIES = icu
 PYTHON_PYICU_SETUP_TYPE = setuptools
 
+PYTHON_PYICU_ENV += \
+	ICU_VERSION="`$(PKG_CONFIG_HOST_BINARY) icu-i18n --modversion`" \
+	PYICU_CFLAGS="`$(PKG_CONFIG_HOST_BINARY) icu-i18n --variable=CXXFLAGS`" \
+	PYICU_LFLAGS="`$(PKG_CONFIG_HOST_BINARY) icu-i18n --libs-only-L` \
+		`$(PKG_CONFIG_HOST_BINARY) icu-i18n --libs-only-l`"
+
 $(eval $(python-package))