tests/tcg: fix constraints in test-i386-adcox

tests/tcg: fix constraints in test-i386-adcox

Clang complains:

  clang -O2 -m64 -mcx16 /home/alex/lsrc/qemu.git/tests/tcg/i386/test-i386-adcox.c -o test-i386-adcox -static
  /home/alex/lsrc/qemu.git/tests/tcg/i386/test-i386-adcox.c:32:26: error: invalid input constraint '0' in asm
          : "r" ((REG)-1), "0" (flags), "1" (out_adcx), "2" (out_adox));
                           ^
  /home/alex/lsrc/qemu.git/tests/tcg/i386/test-i386-adcox.c:57:26: error: invalid input constraint '0' in asm
          : "r" ((REG)-1), "0" (flags), "1" (out_adcx), "2" (out_adox));
                           ^
  2 errors generated.

Pointing out a numbered input constraint can't point to a read/write
output [1]. Convert to a read-only input constraint to allow this.

[1] https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20101101/036036.html

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-16-alex.bennee@linaro.org>