On ARM, in Thumb mode r7 is used for the framepointer; this meant
that we would fail to compile in debug mode because we were using r7
for TCG_AREG0. Shift to r6 instead to avoid this clash.
(Bug reported as LP:870990.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndrzej Zaborowski <andrew.zaborowski@intel.com>