Your xenophobic hatred very much eclipses any rational and legal reasoning you might offer. By your post, you are consumed by hatred so much that you completely rationalize 18USC2441.The Eighth Amendment is part of the Constitution of the United States--not some imaginary constitution of the world. Neither that amendment nor or anything else in the Bill of Rights has ever protected enemy aliens detained abroad by U.S. military forces during time of war. It's revealing that you don't know something as basic as that. The only constitutional protection the Court has ever held the jihadists detained at Guantanamo were entitled to is habeas corpus. See Boumediene v. Bush, 553 U.S. 723 (2008). That right is satisfied by Combatant Status Review Tribunals, which are courtroom proceedings held at Guantanamo.
Whether torture in general violated the Eighth Amendment's prohibition of cruel or unusual punishment would be irrelevant in any case, because none of the enhanced interrogation techniques authorized for use by U.S. officials constituted torture under applicable U.S. laws. Your personal definition of torture, uninformed by those laws, is not relevant to that question.
As I said, the provisions of the 1994 Convention Against Torture U.S. negotiators agreed to were mainly codified in sections 2340, 2340A, and 2340B. Torture is also discussed in some other federal laws, e.g. the war crimes statute you mentioned.
In a just world, many of the jihadist sons of bitches who were captured and detained at Guantanamo would long ago have been tried before military tribunals, convicted, and had their greasy necks stretched on a gallows, with the proceedings broadcast live so their pals overseas could watch, and learn. Being hooded and strung up like a piece of meat is not exactly going out in a blaze of glory. To hell with them, and soon, and may their helpmates join them there.
Any America-hater who has the crying towel out for these war criminals might want to read about how quickly and decisively FDR dealt with a group of Nazi saboteurs captured here in the summer of 1942. A couple books have been written about it. The Supreme Court heard and denied their appeal in Ex Parte Quirin, 317 U.S. 1 (1942). One fine day soon after that, only two months after they had landed here by U-boat, the six convicted war criminals--one of them a U.S. citizen--were taken to a building in New York, and one hour apart, electrocuted.
No surprise here.