cbrotli: add pkg-config directive #877

Job	Run time
Build and test cmake:gcc9	30s
Build and test cmake:clang15	39s
Build and test cmake:clang15:asan	52s
Build and test cmake:clang15:tsan	47s
Build and test cmake:clang15:ubsan	1m 2s
Build and test cmake:qemu-arm-neon-gcc	1m 8s
Build and test cmake-osx:clang	24s
Build and test cmake-osx:gcc	26s
Build and test cmake-win64:msvc-rel	1m 15s
Build and test cmake-win64:msvc-dbg	1m 15s
Build and test fuzz:clang15	34s
Build and test python3.10:clang15	1m 51s
Build and test python3.10-win	54s
Build and test maven	30s
Build and test bazel:root	40s
Build and test bazel:go	1m 1s
Build and test bazel:java	2m 4s
Build and test bazel:research	26s
Build and test bazel-osx:root	45s
Build and test bazel-osx:go	1m 7s
Build and test bazel-osx:java	3m 21s
Build and test bazel-osx:research	47s
Build and test bazel-win:root	1m 20s
Build and test bazel-win:java	3m 35s
Build and test bazel-win:research	1m 26s
	28m 39s

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