Revert "Remove PCRE stiff from package"

This reverts commit 9575daeb685118bc8284019440bf4906bcb0f756.
Add dependencies as external projects

Use the built-in ExternalProject module to add subhook and pcre
as external projects.
Squashed 'deps/subhook/' changes from 868069e..b30c8d5

b30c8d5 Enable install and tests by deafult
3fcaf45 v0.2

git-subtree-dir: deps/subhook
git-subtree-split: b30c8d548d7c1799a6b754916a83966f830fb554
Update subhook