Make libziparchive C++-only.

If we're going to build libziparchive with _FILE_OFFSET_BITS=64, which
seems like a reasonable idea, we don't want off_t/off64_t mixups in the
ABI, and C++ name mangling helps protect against that where C wouldn't.

Bug: N/A
Test: builds
Change-Id: I5f068b41fb4cd9e1e055e5250054318b35bcbc08

include/ziparchive/zip_archive.h

@@ -26,8 +26,6 @@
 #include <sys/types.h>
 #include <utils/Compat.h>
 
-__BEGIN_DECLS
-
 /* Zip compression methods we support */
 enum {
   kCompressStored     = 0,        // no compression
@@ -228,6 +226,4 @@ int32_t ProcessZipEntryContents(ZipArchiveHandle handle, ZipEntry* entry,
         ProcessZipEntryFunction func, void* cookie);
 #endif
 
-__END_DECLS
-
 #endif  // LIBZIPARCHIVE_ZIPARCHIVE_H_