tcg: check CF_PARALLEL instead of parallel_cpus

Thereby decoupling the resulting translated code from the current state
of the system.

The tb->cflags field is not passed to tcg generation functions. So
we add a field to TCGContext, storing there a copy of tb->cflags.

Most architectures have <= 32 registers, which results in a 4-byte hole
in TCGContext. Use this hole for the new field.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/tcg.h

@@ -614,6 +614,7 @@ struct TCGContext {
     uintptr_t *tb_jmp_target_addr; /* tb->jmp_target_arg if !direct_jump */
 
     TCGRegSet reserved_regs;
+    uint32_t tb_cflags; /* cflags of the current TB */
     intptr_t current_frame_offset;
     intptr_t frame_start;
     intptr_t frame_end;