Remove entries about library code from lcov coverage file

Previously coverage data about header files from the C++ library (in /usr) was
included in the lcov coverage report. We want to exclude these files as we are
only interested in coverage of cprover code and excluding library code also
gives a more accurate percentage of overall coverage.

Author: danpoe

Diff for: buildspec-linux-cmake-gcc-cov.yml

@@ -23,6 +23,7 @@ phases:
   post_build:
     commands:
       - lcov --capture --directory build --output-file lcov.info
+      - lcov --remove lcov.info '/usr/*' --output-file lcov.info
       # If $CODEBUILD_SOURCE_VERSION starts with 'pr/', filter out pr number, if not, return empty
       - VCS_PULL_REQUEST=$(echo $CODEBUILD_SOURCE_VERSION | sed '/^pr\//!d;s/^pr\///')
       # If $CODEBUILD_SOURCE_VERSION is commit id, set $VCS_COMMIT_ID

Diff for: buildspec-linux-make-gcc-cov.yml

@@ -34,6 +34,7 @@ phases:
       - make -C jbmc/unit test
       - make -C jbmc/regression test
       - lcov --capture --directory . --output-file lcov.info
+      - lcov --remove lcov.info '/usr/*' --output-file lcov.info
       # If $CODEBUILD_SOURCE_VERSION starts with 'pr/', filter out pr number, if not, return empty
       - VCS_PULL_REQUEST=$(echo $CODEBUILD_SOURCE_VERSION | sed '/^pr\//!d;s/^pr\///')
       # If $CODEBUILD_SOURCE_VERSION is commit id, set $VCS_COMMIT_ID