Revert -ffile-prefix-map usage w/ CMake

[justsmth]

Problem

• Consumers using older GCC compilers (< v8.1) with the AWS_LC_SYS_CMAKE_BUILDER=1 environment variable set experience build failures due to GCC lacking support for the -ffile-prefix-map= option.
• For x86 (32-bit) builds, older GCC compilers do not assume the availability of SSE2. However, SSE2 is required by AWS-LC assembly.

Description of changes:

• Comment out the use of -ffile-prefix-map= for the CMake builder until we have a better solution.
• Sets the -msse2 compiler option on x86 builds that use the "cc" builder.

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 92.52%. Comparing base (c358484) to head (6709e7c).
Report is 78 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #526      +/-   ##
==========================================
- Coverage   95.80%   92.52%   -3.28%     
==========================================
  Files          61       67       +6     
  Lines        8143     9277    +1134     
  Branches        0     9277    +9277     
==========================================
+ Hits         7801     8584     +783     
- Misses        342      422      +80     
- Partials        0      271     +271     

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