Do not use EXPAT_LARGE_SIZE with Emscripten
Results in WASM signature mismatch:
wasm-ld: warning: function signature mismatch: vtkexpat_XML_GetCurrentLineNumber
defined as (i32) -> i32 in /VTK-build/lib/libvtkIOXMLParser-9.1.a(vtkXMLParser.cxx.o) defined as (i32) -> i64 in /VTK-build/lib/libvtkexpat-9.1.a(xmlparse.c.o)
We do not want 64 int's because of limited JavaScript support.