Expose CRC-32 implementation from zlib

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188380 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Compression.cpp b/lib/Support/Compression.cpp
index fd8a874..b5ddb70 100644
--- a/lib/Support/Compression.cpp
+++ b/lib/Support/Compression.cpp
@@ -81,6 +81,10 @@
   return Res;
 }
 
+uint32_t zlib::crc32(StringRef Buffer) {
+  return ::crc32(0, (const Bytef *)Buffer.data(), Buffer.size());
+}
+
 #else
 bool zlib::isAvailable() { return false; }
 zlib::Status zlib::compress(StringRef InputBuffer,
@@ -93,5 +97,8 @@
                               size_t UncompressedSize) {
   return zlib::StatusUnsupported;
 }
+uint32_t zlib::crc32(StringRef Buffer) {
+  llvm_unreachable("zlib::crc32 is unavailable");
+}
 #endif