When the preprocessor encounters an #include statement it now adds
the preprocessor definitions that exist in the included header to its
own set of definitions.
We previously only aggregated the definitions from headers after
processing the source, which was less correct. (For example, there
could be an #ifdef that depends on a definition from another header).
We now call Preprocessor::process_and_lex() and pass the result to the
parser.
Doing the lexing in the preprocessor will allow us to maintain the
original position information of tokens after substituting definitions.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Under some circumstances we need to ignore unsupported preprocessor
keywords instead of crashing the processing, for example during live
parsing in HackStudio.
