Modify RTC.COM to dynamically adjust to hardware

RTC.COM is now one application instead of one per hardware platform.  It
adjusts to the running platform by querying HBIOS for the active
platform.

Source/Apps/Build.cmd

@@ -17,6 +17,7 @@ call :asm Format || goto :eof
 call :asm Talk || goto :eof
 call :asm OSLdr || goto :eof
 call :asm Mode || goto :eof
+call :asm RTC || goto :eof
 
 zx Z80ASM -SYSGEN/F