Set CFLAGS before init'ing cc::Build

[justsmth]

Issues

Addresses:

• AWS_LC_SYS_CFLAGS is ignored when using default ccBuilder #965

Description of changes:

• cc-builder: Move the setting of CFLAGS to before initialization of cc::Build.

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 92.56%. Comparing base (c358484) to head (d4ad274).
⚠️ Report is 293 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #966 +/- ## ========================================== - Coverage 95.80% 92.56% -3.24%  ========================================== Files 61 74 +13 Lines 8143 9893 +1750 Branches 0 9893 +9893 ========================================== + Hits 7801 9157 +1356  - Misses 342 455 +113  - Partials 0 281 +281 

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