FIX: Clang 12 workaround for GCC 4.4

[reneme]

This fixes the clang 12 workaround for GCC 4.4 on the Botan 2.x.x branch. I figure that we won't need this fix for Botan 3.x, right?

[codecov-commenter]

Codecov Report

Merging #2849 (496438e) into release-2 (c55f5d4) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##           release-2    #2849      +/-   ##
=============================================
- Coverage      91.33%   91.32%   -0.02%     
=============================================
  Files            583      583              
  Lines          64188    64188              
  Branches        6291     6287       -4     
=============================================
- Hits           58628    58618      -10     
- Misses          5529     5539      +10     
  Partials          31       31              

Impacted Files	Coverage Δ
src/lib/hash/sha3/sha3.cpp	100.00% <100.00%> (ø)
src/lib/hash/sha3/sha3_bmi2/sha3_bmi2.cpp	100.00% <100.00%> (ø)
src/lib/entropy/rdseed/rdseed.cpp	21.73% <0.00%> (-78.27%)	⬇️
src/cli/cli_rng.cpp	77.35% <0.00%> (-3.78%)	⬇️
src/lib/utils/cpuid/cpuid_x86.cpp	70.58% <0.00%> (-2.95%)	⬇️
src/lib/pubkey/mce/mceliece_key.cpp	85.10% <0.00%> (-1.07%)	⬇️
src/lib/pubkey/dl_group/dl_group.cpp	90.49% <0.00%> (+1.05%)	⬆️
src/lib/misc/cryptobox/cryptobox.cpp	95.71% <0.00%> (+1.42%)	⬆️
src/lib/asn1/der_enc.cpp	83.01% <0.00%> (+2.51%)	⬆️
src/cli/entropy.cpp	92.85% <0.00%> (+4.76%)	⬆️
... and 1 more

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