Clean up AIX makefile to recognize subversions of AIX 4.1 correctly.

This patch is Peter E's, but I'm applying it on his behalf so it'll get
into 7.1RC3 tonight (I'm guessing Peter went to bed already).

src/makefiles/Makefile.aix

@@ -11,7 +11,7 @@ ifneq ($(GCC), yes)
   ifeq ($(host_os), aix3.2.5)
     LDFLAGS_SL = -e _nostart
   endif
-  ifeq ($(host_os), aix4.1)
+  ifneq (,$(findstring aix4.1, $(host_os)))
     LDFLAGS_SL = -bnoentry
   endif
 endif
@@ -29,7 +29,7 @@ $(POSTGRES_IMP):
 ifeq ($(host_os), aix3.2.5)
 	$(MKLDEXPORT) postgres $(bindir) > $@
 else
-  ifeq ($(host_os), aix4.1)
+  ifneq (,$(findstring aix4.1, $(host_os)))
 	$(MKLDEXPORT) postgres $(bindir) > $@
   else
 	$(MKLDEXPORT) postgres . > $@