Detect compiler architecture at configure time

[randombit]

Avoids build confusions like #1442

[codecov-io]

Codecov Report

Merging #1443 into master will decrease coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1443      +/-   ##
==========================================
- Coverage   92.54%   92.18%   -0.37%     
==========================================
  Files         469      469              
  Lines       44199    44199              
  Branches     5330     5330              
==========================================
- Hits        40906    40743     -163     
- Misses       3261     3424     +163     
  Partials       32       32

Impacted Files	Coverage Δ
.../block/threefish/threefish_avx2/threefish_avx2.cpp	0% <0%> (-100%)	⬇️
src/lib/pubkey/xmss/xmss_privatekey.cpp	64.06% <0%> (-22.66%)	⬇️
src/lib/utils/cpuid/cpuid_x86.cpp	78.84% <0%> (-3.85%)	⬇️
src/lib/pk_pad/emsa_raw/emsa_raw.cpp	72.22% <0%> (-2.78%)	⬇️
src/lib/tls/msg_server_hello.cpp	88.76% <0%> (-1.13%)	⬇️
src/lib/block/threefish/threefish.cpp	90.81% <0%> (-1.03%)	⬇️
src/lib/tls/tls_algos.cpp	76.72% <0%> (-0.87%)	⬇️
src/lib/tls/tls_extensions.cpp	86.5% <0%> (-0.35%)	⬇️
src/lib/pubkey/xmss/xmss_tools.cpp	97.05% <0%> (ø)	⬆️

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