Replace ukbhit by kbd_enter_pressed, not requiring tcgetattr:

Note that it behaves differently now
* it looks for Enter key only, not any key
* it "eats" the input, no need for (void)getchar() after it
* it works the same no matter the value of ICANON
* the mingw version has been adapted to act the similarly

This should fix its usage on Android where tcgetattr always returns -1

client/scripts/tracetest.lua

@@ -118,7 +118,7 @@ local function main(args)
 
         core.clearCommandBuffer()
 
-        if core.ukbhit() then
+        if core.kbd_enter_pressed() then
             print('aborted by user')
             break
         end