target-arm: Clear IT bits when taking exceptions in v7M

When taking an exception for an M profile core, we must clear
the IT bits. Since the IT bits are cached in env->condexec_bits
we must clear them there: writing the bits in env->uncached_cpsr
has no effect. (Reported as LP:944645.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/helper.c

@@ -877,7 +877,8 @@ static void do_interrupt_v7m(CPUARMState *env)
     v7m_push(env, env->regs[1]);
     v7m_push(env, env->regs[0]);
     switch_v7m_sp(env, 0);
-    env->uncached_cpsr &= ~CPSR_IT;
+    /* Clear IT bits */
+    env->condexec_bits = 0;
     env->regs[14] = lr;
     addr = ldl_phys(env->v7m.vecbase + env->v7m.exception * 4);
     env->regs[15] = addr & 0xfffffffe;