Fix pkg-config files

[skmcgrail]

Description of changes:

Discovered that our pkg-config description files had hard-coded libdir and includedir values that could differ from the actual installation directory values.

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 78.47%. Comparing base (36e0307) to head (80c1adb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1890      +/-   ##
==========================================
- Coverage   78.50%   78.47%   -0.03%     
==========================================
  Files         585      585              
  Lines       99516    99516              
  Branches    14244    14243       -1     
==========================================
- Hits        78122    78097      -25     
- Misses      20759    20783      +24     
- Partials      635      636       +1     

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