use a form that please /bin/dash in apache_commons build script

Change-Id: I2a7061f428d402751627fc93ca559e119aab94d2

apache-commons/ExternalProject_apache_commons_codec.mk

@@ -20,7 +20,7 @@ $(eval $(call gb_ExternalProject_register_targets,apache_commons_codec,\
 
 $(call gb_ExternalProject_get_state_target,apache_commons_codec,build) :
 	cd "$(call gb_UnpackedTarball_get_dir,apache_commons_codec)" && \
-	ANT_OPTS+="-Dfile.encoding=ISO-8859-1" \
+	ANT_OPTS="$$ANT_OPTS -Dfile.encoding=ISO-8859-1" \
 	"$(ANT)" \
 		-q \
 		-f build.xml \

apache-commons/ExternalProject_apache_commons_httpclient.mk

@@ -23,7 +23,7 @@ $(eval $(call gb_ExternalProject_register_targets,apache_commons_httpclient,\
 
 $(call gb_ExternalProject_get_state_target,apache_commons_httpclient,build) :
 	cd "$(call gb_UnpackedTarball_get_dir,apache_commons_httpclient)" && \
-	ANT_OPTS+="-Dfile.encoding=ISO-8859-1" \
+	ANT_OPTS="$$ANT_OPTS -Dfile.encoding=ISO-8859-1" \
 	"$(ANT)" \
 		-q \
 		-f build.xml \

apache-commons/ExternalProject_apache_commons_lang.mk

@@ -20,7 +20,7 @@ $(eval $(call gb_ExternalProject_register_targets,apache_commons_lang,\
 
 $(call gb_ExternalProject_get_state_target,apache_commons_lang,build) :
 	cd "$(call gb_UnpackedTarball_get_dir,apache_commons_lang)" && \
-	ANT_OPTS+="-Dfile.encoding=ISO-8859-1" \
+	ANT_OPTS="$$ANT_OPTS -Dfile.encoding=ISO-8859-1" \
 	"$(ANT)" \
 		-q \
 		-f build.xml \

apache-commons/ExternalProject_apache_commons_logging.mk

@@ -20,7 +20,7 @@ $(eval $(call gb_ExternalProject_register_targets,apache_commons_logging,\
 
 $(call gb_ExternalProject_get_state_target,apache_commons_logging,build) :
 	cd "$(call gb_UnpackedTarball_get_dir,apache_commons_logging)" && \
-	ANT_OPTS+="-Dfile.encoding=ISO-8859-1" \
+	ANT_OPTS="$$ANT_OPTS -Dfile.encoding=ISO-8859-1" \
 	"$(ANT)" \
 		-q \
 		-f build.xml \