python3: force ac_cv_working_tzset=yes.

The check for it fails by default when cross-compiling, which
results in missing time.tzset.

srcpkgs/python3/template

@@ -4,7 +4,7 @@
 #
 pkgname=python3
 version=3.9.6
-revision=1
+revision=2
 wrksrc="Python-${version}"
 pycompile_dirs="usr/lib/python${version%.*}"
 hostmakedepends="pkgconf"
@@ -49,7 +49,8 @@ do_configure() {
 	./configure ${configure_args} ${_args} \
 		--enable-shared --enable-ipv6 --enable-loadable-sqlite-extensions \
 		--with-computed-gotos --with-dbmliborder=gdbm:ndbm \
-		--with-system-expat --with-system-ffi --without-ensurepip
+		--with-system-expat --with-system-ffi --without-ensurepip \
+		ac_cv_working_tzset=yes
 }
 
 do_build() {