From master cherry-pick/backport to 1.11 branch

[NIIBE Yutaka]

Hello,

If no objections, for LIBGCRYPT-1.11-BRANCH,

I'd like to backport the master commit of:

    1003c941 * Add stack burning for PQC algorithms

Also I'd like to cherry-pick the commits of

the const-time thingy:

    11e8f4a8 * const-time: add 64-bit fast paths for const-time buffer functions
    4c253746 * mceliece6688128f: use const-time helper for memory comparison
    4012e9a0 * mceliece6688128f: harden mask generation against branch optimization
    4e963e91 * sntrup761: use const-time helpers for memory comparison and cond move
    bf7546c5 * sntrup761: harden mask generation against branch optimization
    052b03fb * kyber: harden mask generation against branch optimization
    96534d8c * mpih-pow: harden condition calculation against branch optimization
    ee5cb383 * cipher-xts: harden mask generation against branch optimization
    f6b7a40f * rijndael: harden mask generation against branch optimization

and fixes for:

    5bd93201 * mceliece6688128f: fix stack overflow crash on win64/wine
    a786e3b6 * mceliece6688128f: fix UBSAN runtime errors

and build clean up for portability:

    371e1f1f * Update autogen.sh also for test(1) -o adjustment.
    e9019e32 * Adjust scripts for test(1) operator -a removal
    ce034f72 * Update autogen.sh and gpg-error.m4 from upstream.

and a fix for a test program:

    9f26fa62 * t-kem: fix test loop iteration
--