Provide amalgamated source for the C shared library

[ddiproietto]

Similar to how we provide an amalgamated source for the C++ library, we should provide an amalgamated source for the C shared library.

[MarijnS95]

On the fly compiling and statically linking the C bindings is exactly what I need to bind Perfetto to Rust. That'll be much more convenient than pre-compiling and bundling libperfetto_c.so for various targets/architectures.

As a temporary workaround, would it be possible to compile perfetto_c statically, so that I don't have to move around and ship .so/.dlls?

Going forward, I see a few things in the C bindings that still need to change to make them fully usable for this use-case (Rust, without #includeing the the headers in a C project). Some of these points should likely be split out into separate issues:

• Improved documentation and samples for the raw C bindings. My Rust bindings are based on dissecting the implementations of various macros and static inline functions used in examples/shared_lib/ files;
• Said static inline functions need to become exported functions, otherwise they need to be reimplemented in Rust based on (hopefully!) exported functions that are called inside;
  • One example is PerfettoTeCounterTrackRegister(), which I think is required to make counters work, i.e. they cannot be reported on the current process/thread track?;
  • Other examples are various static inline functions that end up calling lower-level *Impl() functions;
• Will this become a second, separate amalgamated source file? The current perfetto.cc file takes very long to compile, and probably includes far too many sources that won't be needed for the C bindings;
• Good documentation of when (pointers to) data outlive a function call. This seems to be the case specifically when registering categories but (obviously) not when emitting trace markers.