missing BLARGG_EXPORT macros actually added to gme.h

[hmaon]

a comment on one of the most recent commits indicates that BLARGG_EXPORT macros should already be in gme.h but they're not there and gme.h is untouched in that commit

This change fixes gme.h

[connorjclark]

FYI, this fixed my errors w/ building the lib. redefinition; different linkage. thanks!