Validate or define ARM HWCAP2_XXX macros

[justsmth]

Issues:

Addresses: aws/aws-lc-rs#681

Description of changes:

On some platforms ARM's HWCAP2_XXX macros might be defined in system header files, causing compilation failure due to their being redefined here.

.../aws-lc/crypto/fipsmodule/cpucap/cpu_arm_linux.h:35:9: error: 'HWCAP2_AES' redefined [-Werror]
     35 | #define HWCAP2_AES (1 << 0)
        |         ^~~~~~~~~~
  In file included from .../armv7ve-libreelec-linux-gnueabihf/sysroot/usr/include/bits/hwcap.h:53:9: note: this is the location of the previous definition
     53 | #define HWCAP2_AES              1
        |         ^~~~~~~~~~

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.96%. Comparing base (cc9c9f0) to head (4aaf4ad).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2164      +/-   ##
==========================================
- Coverage   78.97%   78.96%   -0.01%     
==========================================
  Files         611      611              
  Lines      105552   105551       -1     
  Branches    14950    14950              
==========================================
- Hits        83361    83352       -9     
- Misses      21538    21547       +9     
+ Partials      653      652       -1     

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