The INCLUDE variable being used during `.rc` preprocessing was an accidental regression in https://github.com/ziglang/zig/pull/17412.
Closes #17585.

resinator changes:
source_mapping: Protect against NUL bytes in #line filenames
lex: Avoid recalculating column on every tab stop within string literals
Proper error handling for failing to open cwd instead of `catch unreachable`
Use platform-specific delimiter for INCLUDE env var parsing