tcg/i386: Set P_REXW in tcg_out_addi_ptr

The REXW bit must be set to produce a 64-bit pointer result; the
bit is disabled in 32-bit mode, so we can do this unconditionally.

Fixes: 7d9e1ee4 ("tcg/i386: Adjust assert in tcg_out_addi_ptr")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1592
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1642


Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 98899850

)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>