Add openjpeg pre-processor OPJ_STATIC to pdfium.gyp

Openjpeg removed the definition of OPJ_STATIC in openjpeg.h.
This change is merged in https://pdfium.googlesource.com/pdfium/+/d53e6fdb0a86ca1ddb12876a60f7f2d7508b5349
So need to add OPJ_STATIC to pdfium.gyp

BUG=None
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/624043002