iOS, codesigning .dylib

.dylib can only be loaded if signed, so added
codesign to make

In order not to expose the code identity, this is added through
use of an environment variable IOS_CODESIGN

Change-Id: I03ee7a6f2bfa8493a08b3e90163ab6c68d3c94a9

ios/CustomTarget_iOS_prelink.mk

@@ -64,6 +64,13 @@ $(IOSKIT): $(WORKDIR)/CObject/ios/source/LibreOfficeKit.o
 	    $(WORKDIR)/CObject/ios/source/LibreOfficeKit.o \
 	    `$(SRCDIR)/bin/lo-all-static-libs` \
 	    -o $(IOSKIT)
+ifeq ($(origin IOS_CODEID),undefined)
+	@echo "please define environment variable IOS_CODEID as\n" \
+	      "export IOS_CODEID=<your apple code identifier>"
+	@exit -1
+else
+	codesign -s "$(IOS_CODEID)" $(IOSKIT) 
+endif