Add some macros to easily allow users to hook into the tracing system
Add some macros to easily allow users to hook into the tracing system

Because these are simple RAII structs intended to be used directly, they
can't be expected to be subclassed, and users would end up having to
redefine their implementation in a modified version of this header.

apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild