must give hint to libtool which tag to use, in case we use ccache and then
libtool is unable to autodetect from $CC

--- apr-1.5.0/configure.in.orig	2013-11-22 17:29:57.303051538 +0100
+++ apr-1.5.0/configure.in	2013-11-22 17:31:11.273048433 +0100
@@ -280,9 +280,9 @@
   [ use_libtool=$withval ], [ use_libtool="yes" ] )
 
 if test "x$use_libtool" = "xyes"; then
-      lt_compile='$(LIBTOOL) $(LTFLAGS) --mode=compile $(COMPILE) -o $@ -c $< && touch $@'
+      lt_compile='$(LIBTOOL) $(LTFLAGS) --mode=compile --tag=CC $(COMPILE) -o $@ -c $< && touch $@'
       LT_VERSION="-version-info `$get_version libtool $version_hdr APR`"
-      link="\$(LIBTOOL) \$(LTFLAGS) --mode=link \$(COMPILE) \$(LT_LDFLAGS) \$(LT_VERSION) \$(ALL_LDFLAGS) -o \$@"
+      link="\$(LIBTOOL) \$(LTFLAGS) --mode=link --tag=CC \$(COMPILE) \$(LT_LDFLAGS) \$(LT_VERSION) \$(ALL_LDFLAGS) -o \$@"
       so_ext='lo'
       lib_target='-rpath $(libdir) $(OBJECTS)'
       export_lib_target='-rpath \$(libdir) \$(OBJECTS)'