Properly fix Lex/Yacc dependency following Ingo's advice

* By setting HDRGRIST to match SOURCE_GRIST in MultiArchDirSetup, the
include scanning in Jam will work properly: the generated header will
have the same grist as what the include scan looks for.
* Remove the now unneeded workaround from netresolv Jamfile.

build/jam/ArchitectureRules

@@ -739,10 +739,13 @@ rule MultiArchSubDirSetup architectures
 			$(var) on $(architectureObject) = $($(var)) ;
 		}
 
-		# adjust SOURCE_GRIST
+		# adjust SOURCE_GRIST and HDRGRIST
 		SOURCE_GRIST on $(architectureObject)
 			= $(SOURCE_GRIST:E=)!$(architecture) ;
 
+		HDRGRIST on $(architectureObject)
+			= $(HDRGRIST:E=)!$(architecture) ;
+
 		# Adjust the subdir's object dirs that are architecture dependent. To
 		# avoid duplicating the code from SetupObjectsDir, we call it. Since it
 		# sets global variables, we set these variables on our object, call