poppler: suppress warnings

    rbpoppler-annotationmarkup.c: In function 'Init_poppler_annotationmarkup':
    rbpoppler-annotationmarkup.c:87:5: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]

    rbpoppler-fontsiter.c: In function 'Init_poppler_fontsiter':
    rbpoppler-fontsiter.c:112:5: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]