[PATCH, ARM] Don't use __thumb2__ to select _REENT_SMALL

[Paul Brook]

> Yes, this leaks out into user code -- at least it does for me.  Try
> building the standard arm-eabi multilib tools and then running the gcc
> testsuite with -mcpu=cortex-a8 and -mthumb.  Programs such as
> gcc.c-torture/exectute/fprintf-1.c will then fail.
>
> The definition of stdout is:
> #define stdout  (_REENT->_stdout)

In my sources this field lives at the same location in both cases.

Paul