New macro XXC is like XXO but with a context (and really same as XC)

locale/update_po_files.sh

@@ -5,7 +5,7 @@ sed -E 's/\.\.\///g' |\
 xargs xgettext \
 --default-domain=audacity \
 --directory=.. \
---keyword=_ --keyword=XO --keyword=XC:1,2c --keyword=XXO --keyword=XP:1,2 --keyword=XPC:1,2,4c \
+--keyword=_ --keyword=XO --keyword=XC:1,2c --keyword=XXO --keyword-XXC:1,2c --keyword=XP:1,2 --keyword=XPC:1,2,4c \
 --add-comments=" i18n" \
 --add-location=file  \
 --copyright-holder='Audacity Team' \

src/Internat.h

@@ -45,6 +45,9 @@ extern AUDACITY_DLL_API const wxString& GetCustomSubstitution(const wxString& st
 // might use the & character for shortcuts.
 #define XXO(s)  XO(s)
 
+// Corresponds to XC as XXO does to XO
+#define XXC(s, c) XC(s, c)
+
 #ifdef _
    #undef _
 #endif