Provides macros for properly exporting or importing symbols from shared libraries.
COMPONENT_BUILD is defined when generating shared libraries for each project, rather than static libraries. This means we need to be careful about EXPORT/IMPORT. SB_IS_LIBRARY is defined when building Starboard as a shared library to be linked into a client app. In this case, we want to explicitly define EXPORT/IMPORT so that Starboard's symbols are visible to such clients.