chore(CI): add portable mode to qmake build

Resolve https://github.com/BLumia/pineapple-pictures/issues/148

This change is sponsored by @EdgarHartel.

pineapple-pictures.pro

@@ -9,6 +9,10 @@ TARGET = ppic
 TEMPLATE = app
 DEFINES += PPIC_VERSION_STRING=\\\"x.y.z\\\"
 
+win32 {
+    DEFINES += FLAG_PORTABLE_MODE_SUPPORT=1
+}
+
 # The following define makes your compiler emit warnings if you use
 # any feature of Qt which has been marked as deprecated (the exact warnings
 # depend on your compiler). Please consult the documentation of the