package/tcl: fix for POSIX compliance

Using two '=' for string comparison is a bashism.
Revert to using one, as stated in POSIX 1003.1-2008.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/tcl/tcl.mk

@@ -15,10 +15,10 @@ TCL_CONF_OPT = \
 
 define TCL_POST_INSTALL_CLEANUP
 	-$(STRIPCMD) $(STRIP_STRIP_UNNEEDED) $(TARGET_DIR)/usr/lib/libtcl8.4.so
-	-if [ "$(BR2_PACKAGE_TCL_DEL_ENCODINGS)" == "y" ]; then \
+	-if [ "$(BR2_PACKAGE_TCL_DEL_ENCODINGS)" = "y" ]; then \
 	rm -Rf $(TARGET_DIR)/usr/lib/tcl8.4/encoding/*; \
 	fi
-	-if [ "$(BR2_PACKAGE_TCL_SHLIB_ONLY)" == "y" ]; then \
+	-if [ "$(BR2_PACKAGE_TCL_SHLIB_ONLY)" = "y" ]; then \
 	rm -f $(TARGET_DIR)/usr/bin/tclsh8.4; \
 	fi
 endef