Fix rapid7#5335, resolve metasm parsing issues in x64 exitfunk

Author: HD Moore

lib/msf/core/payload/windows/x64/exitfunk.rb

@@ -40,14 +40,14 @@ def asm_exitfunk(opts={})
         mov r10d, 0x9DBD95A6  ; hash( "kernel32.dll", "GetVersion" )
         call rbp              ; GetVersion(); (AL will = major version and AH will = minor version)
         add rsp, 40           ; cleanup the default param space on stack
-        cmp al, byte 6        ; If we are not running on Windows Vista, 2008 or 7
-        jl short goodbye      ; Then just call the exit function...
+        cmp al, 6             ; If we are not running on Windows Vista, 2008 or 7
+        jl exitfunk_goodbye   ; Then just call the exit function...
         cmp bl, 0xE0          ; If we are trying a call to kernel32.dll!ExitThread on
                               ; Windows Vista, 2008 or 7...
-        jne short goodbye     ;
+        jne exitfunk_goodbye  ;
         mov ebx, 0x6F721347   ; Then we substitute the EXITFUNK to that of ntdll.dll!RtlExitUserThread
-      goodbye:                ; We now perform the actual call to the exit function
-        push byte 0           ;
+      exitfunk_goodbye:       ; We now perform the actual call to the exit function
+        push 0                ;
         pop rcx               ; set the exit function parameter
         mov r10d, ebx         ; place the correct EXITFUNK into r10d
         call rbp              ; call EXITFUNK( 0 );