build: add /usr/local/ to LCOV_FILTER_PATTERN for macOS builds
build: add /usr/local/ to LCOV_FILTER_PATTERN for macOS builds

With this commit, the files in /usr/local/ will not be included in
`make cov` or `make cov_fuzz` coverage reports. This behavior could
be observed when generating the reports on macOS with brew-installed
clang.


Former-commit-id: 590c6a653b865eef6689ec94cfd29a9efd827226
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin