MFH: r561570
graphics/pdfpc: fix build on GCC architectures
In file included from /usr/local/include/webkitgtk-4.0/jsc/jsc.h:25,
from /usr/local/include/webkitgtk-4.0/webkit2/WebKitJavascriptResult.h:28, from /usr/local/include/webkitgtk-4.0/webkit2/webkit2.h:57, from src/classes/view/markdown.c:4:
/usr/local/include/webkitgtk-4.0/jsc/JSCClass.h:37: error: redefinition of typedef 'JSCClass'
/usr/local/include/webkitgtk-4.0/jsc/JSCValue.h:43: error: previous declaration of 'JSCClass' was here
/usr/local/include/webkitgtk-4.0/jsc/JSCClass.h:40: error: redefinition of typedef 'JSCContext'
/usr/local/include/webkitgtk-4.0/jsc/JSCValue.h:44: error: previous declaration of 'JSCContext' was here