[DeLICM/ZoneAlgo] Remove duplicate code. NFC.

DeLICM and ZoneAlgo both implemented filterKnownValInst.

Declare ZoneAlgo's version in the header and let DeLCIM use it.

llvm-svn: 310381
diff --git a/polly/lib/Transform/ZoneAlgo.cpp b/polly/lib/Transform/ZoneAlgo.cpp
index d8618a5..70105f5 100644
--- a/polly/lib/Transform/ZoneAlgo.cpp
+++ b/polly/lib/Transform/ZoneAlgo.cpp
@@ -246,12 +246,7 @@
          Space.is_wrapping().is_false() && Space.dim(isl::dim::set) == 0;
 }
 
-/// Return only the mappings that map to known values.
-///
-/// @param UMap { [] -> ValInst[] }
-///
-/// @return { [] -> ValInst[] }
-static isl::union_map filterKnownValInst(const isl::union_map &UMap) {
+isl::union_map polly::filterKnownValInst(const isl::union_map &UMap) {
   isl::union_map Result = isl::union_map::empty(UMap.get_space());
   UMap.foreach_map([=, &Result](isl::map Map) -> isl::stat {
     if (!isMapToUnknown(Map))