Fix OS X build at least with current tool-chain

Pass correct -I flag to acloal in the ACLOCAL environemnt variable,
and set that environment variable for the running of autoreconf for it
it to have any effect.

Change-Id: I64238b6b96539dff28c2ddc16cc17f18ebb22129

libxmlsec/ExternalProject_xmlsec.mk

@@ -44,10 +44,9 @@ else
 
 $(call gb_ExternalProject_get_state_target,xmlsec,build) :
 	cd $(EXTERNAL_WORKDIR) \
-	&& autoreconf \
-	&& $(if $(filter MACOSX,$(OS)),ACLOCAL="aclocal -I $(EXTERNAL_WORKDIR)/m4/mac") \
-	./configure \
-	--with-pic --disable-shared --disable-crypto-dl --without-libxslt --without-gnutls \
+	&& $(if $(filter MACOSX,$(OS)),ACLOCAL="aclocal -I $(SRCDIR)/m4/mac") autoreconf \
+	&& ./configure \
+		--with-pic --disable-shared --disable-crypto-dl --without-libxslt --without-gnutls \
 	$(if $(filter ANDROID,$(OS)),--with-openssl=$(OUTDIR),--without-openssl) \
 	$(if $(filter MACOSX,$(OS)),--prefix=/@.__________________________________________________OOO) \
 	$(if $(filter NO,$(SYSTEM_NSS))$(filter MACOSX,$(OS)),--disable-pkgconfig) \