Further reduce amount of symbols exported from static orcus library

Following up on 7a4cc197 "Also on Linux do not
export symbols from static orcus libraries" that turned out to not be enough to
prevent ASan ODR violation reports after
f0aa1a78 "For Clang -fsanitize=vptr use
-fvisibility-ms-compat, not -fvisibility=hidden."  Given that liborcus is only
ever linked in as a static archive, it is hopefully OK (intended, even?) to not
export any of its symbols.

Change-Id: Ib8eb084def1725374747a389065bf8186218786e

external/liborcus/liborcus_0.1.0-dllimport.patch

@@ -18,7 +18,7 @@
  #else
    #if __GNUC__ >= 4
 -    #define ORCUS_DLLPUBLIC __attribute__ ((visibility ("default")))
-+    #define ORCUS_DLLPUBLIC
++    #define ORCUS_DLLPUBLIC __attribute__ ((visibility ("hidden")))
      #define ORCUS_DLLLOCAL  __attribute__ ((visibility ("hidden")))
    #else
      #define ORCUS_DLLPUBLIC