Model compiler flags better for compiler feature probing

[torben-hansen]

Issues:

CryptoAlg-1476

Description of changes:

Compiler flags are not yet populated during compiler feature probing for gcc/clang. Better model compiler flags during compiler feature probing by moving the probing to succeed it.

This also better models the bb environment.

Also fix-up comments for all feature probes and correct some issues discovered when adding more compiler diagnostics.

In addition, attempting to prevent build applications interpreting negative feature probes as build errors.

Output changes below

Before

-- Test stdalign_check.c passed, enabling AWS_LC_STDALIGN_AVAILABLE
-- Test builtin_swap_check.c failed, NOT enabling AWS_LC_BUILTIN_SWAP_SUPPORTED:
--     Change Dir: /home/ec2-user/humble/aws-lc/awslc-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja-build" "cmTC_4a755"
[1/2] Building C object CMakeFiles/cmTC_4a755.dir/builtin_swap_check.c.o
FAILED: CMakeFiles/cmTC_4a755.dir/builtin_swap_check.c.o 
/[...]
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/builtin_swap_check.c: In function ‘main’:
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/builtin_swap_check.c:20:1: error:

After

-- stdalign_check.c probe is positive, enabling AWS_LC_STDALIGN_AVAILABLE
-- builtin_swap_check.c probe is negative, NOT enabling AWS_LC_BUILTIN_SWAP_SUPPORTED:
--     Change Dir: /home/ec2-user/humble/aws-lc/awslc-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja-build" "cmTC_83977"
[1/2] Building C object CMakeFiles/cmTC_83977.dir/builtin_swap_check.c.o
FAILED: CMakeFiles/cmTC_83977.dir/builtin_swap_check.c.o 
/[...]
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/builtin_swap_check.c: In function ‘main’:
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/builtin_swap_check.c:20:1: compiler_error:

Testing:

See CryptoAlg-1476 for some additional tests.

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.