To avoid noise due to local C files when using automatic local checksrc
checks (e.g. via CMake `-DCURL_LINT=ON` option, or `curl-lint` target).
Also replace single-quote with double-quote in external git command, for
portability.
Follow-up to 88ff396549#17882
Follow-up to e785e898a6#17376Closes#20439
To make the test files XML-compliant, and the expected results
possibly easier to manage by keeping them in `.c` files.
Non-XML-compliant files are down to 36 after this patch.
Also:
- make all macro expansions apply to `%includetext` contents.
Closes#19799
`checksrc.bat` was outdated and required Perl for `checksrc.pl` anyway.
Rewrite `checksrc-all.sh` in Perl, making it usable in envs without
a POSIX shell.
Closes#17882
