Document missing build steps

[randomPoison]

In integrating IA2 into zlib I uncovered a number of build steps that aren't currently covered in the docs. We'll need to update the docs to include the following:

• How to run the rewriter, i.e. source changes, compiler args, and rewriter args.
• partition-alloc needs to be included in the final containerized build, and the --wrap=malloc linker args need to be added.
• Either LIBIA2_X86_64 or LIBIA2_ARM64 defines need to be set for the containerized build.
• Run pad-tls on any shared objects that use TLS. We probably also want to document how to determine if a .so uses TLS.

[kkysen]

Either LIBIA2_X86_64 or LIBIA2_ARM64 defines need to be set for the containerized build.

This is fixed as of #400.

[ayrtonm]

We probably also want to document how to determine if a .so uses TLS.

We were thinking about adding runtime checks for this in #404, so we can also point users to the right readelf flags in that error message.

[ayrtonm]

partition-alloc needs to be included in the final containerized build, and the --wrap=malloc linker args need to be added.

It might be a good idea to runtime checks for this as well.

[ayrtonm]

The names of -DIA2_DEBUG and -DIA2_DEBUG_LOG are also too similar. After addressing #452 the former will probably be -DIA2_RELEASE with inverted semantics and we should consider renaming the former to something like -DIA2_VERBOSE or -DIA2_LOG since that seems more descriptive than "debug".

[kkysen]

The names of -DIA2_DEBUG and -DIA2_DEBUG_LOG are also too similar. After addressing #452 the former will probably be -DIA2_RELEASE with inverted semantics and we should consider renaming the former to something like -DIA2_VERBOSE or -DIA2_LOG since that seems more descriptive than "debug".

-DIA2_VERBOSE sounds good to me.