tccrun/win64: cleanup runtime function table

- call RtlDeleteFunctionTable
  (important for multiple compilations)

- the RUNTIME_FUNCTION* is now at the beginning of the
  runtime memory.  Therefor when tcc_relocate is called
  with user memory, this should be done manually before
  it is free'd:
      RtlDeleteFunctionTable(*(void**)user_mem);
      [ free(user_mem); ]

- x86_64-gen.c: expand char/short return values to int

win32/lib/kernel32.def

@@ -552,6 +552,7 @@ ResetNLSUserInfoCache
 ResetWriteWatch
 ResumeThread
 RtlAddFunctionTable
+RtlDeleteFunctionTable
 RtlFillMemory
 RtlInstallFunctionTableCallback
 RtlMoveMemory