src/tk/tkevent.c: Micropolis build fixes for recent macOS

src/tk/tkevent.c: Micropolis build fixes for recent macOS

Fix:
tkevent.c:682:3: error: implicit declaration of function 'TkWmProtocolEventProc' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                TkWmProtocolEventProc(winPtr, eventPtr);
                ^
tkevent.c:1447:5: error: implicit declaration of function 'Tcl_CheckForSignal' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (Tcl_CheckForSignal (tk_mainInterp, TCL_OK) == TCL_ERROR)
    ^
tkevent.c:1512:5: error: implicit declaration of function 'Tcl_CheckForSignal' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (Tcl_CheckForSignal (tk_mainInterp, TCL_OK) == TCL_ERROR)
    ^