Use system AR.

Gentoo bug #461254.

--- lib/Makefile
+++ lib/Makefile
@@ -53,7 +53,7 @@
 	    -rpath $(PATHLIB) -version-info 2:0:0
 
 libinn.a: $(OBJECTS)
-	ar r $@ $(OBJECTS)
+	$(AR) r $@ $(OBJECTS)
 	$(RANLIB) libinn.a
 
 .c.o .c.lo:
--- storage/Makefile
+++ storage/Makefile
@@ -55,7 +55,7 @@
 	    -rpath $(PATHLIB) -version-info 2:0:0
 
 libstorage.a: $(OBJECTS)
-	ar r $@ $(OBJECTS)
+	$(AR) r $@ $(OBJECTS)
 	$(RANLIB) libstorage.a
 
 # Make.methods is included in the distribution tarball since some non-GNU
--- history/Makefile
+++ history/Makefile
@@ -51,7 +51,7 @@
 	    -rpath $(PATHLIB) -version-info 2:0:0
 
 libinnhist.a: $(OBJECTS)
-	ar r $@ $(OBJECTS)
+	$(AR) r $@ $(OBJECTS)
 	$(RANLIB) libinnhist.a
 
 # Try to set up these rules so that buildconfig is only run once.