target-i386: Fix SSE status flag corruption

When we restore the mxcsr register with FXRSTOR, or set it with gdb,
we need to update the various SSE status flags in CPUX86State

Reported-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
diff --git a/target-i386/gdbstub.c b/target-i386/gdbstub.c
index 15bebef..d34e535 100644
--- a/target-i386/gdbstub.c
+++ b/target-i386/gdbstub.c
@@ -222,7 +222,7 @@
             return 4;
 
         case IDX_MXCSR_REG:
-            env->mxcsr = ldl_p(mem_buf);
+            cpu_set_mxcsr(env, ldl_p(mem_buf));
             return 4;
         }
     }