Define a dummy zlib::uncompress when zlib is not available.

Should fix link errors in some bots when it is used.

llvm-svn: 281208
diff --git a/llvm/lib/Support/Compression.cpp b/llvm/lib/Support/Compression.cpp
index 7453071..5d55646 100644
--- a/llvm/lib/Support/Compression.cpp
+++ b/llvm/lib/Support/Compression.cpp
@@ -94,6 +94,10 @@
                             CompressionLevel Level) {
   return zlib::StatusUnsupported;
 }
+zlib::Status zlib::uncompress(StringRef InputBuffer, char *UncompressedBuffer,
+                              size_t &UncompressedSize) {
+  return zlib::StatusUnsupported;
+}
 zlib::Status zlib::uncompress(StringRef InputBuffer,
                               SmallVectorImpl<char> &UncompressedBuffer,
                               size_t UncompressedSize) {