Only export public symbols.

[ Merge of http://go/wvgerrit/67923 ]

Before, all symbols were being exported in the dynamic library.  Now
only the public symbols are.  This no longer has the unit tests load
the dynamic library, so we lose testing the dynamic integration; but
the unit tests use a lot of internals, even the top-level CDM ones.

Bug: 69271232
Bug: 69548115
Test: WV unit/integration tests
Change-Id: I62919937277ec785aca1f8b36b28caa2f9d8f3ea

libwvdrmengine/cdm/util/include/util_common.h

@@ -0,0 +1,22 @@
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
+
+#ifndef WVCDM_UTIL_UTIL_COMMON_H_
+#define WVCDM_UTIL_UTIL_COMMON_H_
+
+#ifdef _WIN32
+# ifdef CORE_UTIL_IMPLEMENTATION
+#  define CORE_UTIL_EXPORT __declspec(dllexport)
+# else
+#  define CORE_UTIL_EXPORT __declspec(dllimport)
+# endif
+#else
+# ifdef CORE_UTIL_IMPLEMENTATION
+#  define CORE_UTIL_EXPORT __attribute__((visibility("default")))
+# else
+#  define CORE_UTIL_EXPORT
+# endif
+#endif
+
+#endif  // WVCDM_UTIL_UTIL_COMMON_H_