[S] Change in coreboot[master]: util/cbmem: Add REG_NEWLINE flag to fix matching pattern

[Konrad Adamczyk (Code Review)]

Attention is currently required from: Raul Rangel, Jakub Czapiga, Grzegorz Bernacki.

Konrad Adamczyk has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74742 )

Change subject: util/cbmem: Add REG_NEWLINE flag to fix matching pattern
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Patch Set 1:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/74742/comment/ac069d44_59a6ad4e 
PS1, Line 13: REG_NEWLINE
> How was this working before? Did we change the banner?

TL;DR: 
`How was this working before?` - Match occured not on the first line, but until `Starting kernel...` log (basically, whole boot log).
`Did we change the banner?` - Change of BANNER_REGEX was introduced in https://review.coreboot.org/c/coreboot/+/62720.

`-- Long version stars here --`:
Before this CL, if `cbmem` buffer contained logs from two boots, match for regex occured three times:
1. Whole boot log (from `coreboot-` till `Starting kernel...` where three dots at the end matched BANNER_REGEX),
2. Second boot log (from `coreboot-` till `Starting kernel...`) (due to `.?`)
3. Second boot log again (from `coreboot-` till `Starting kernel...`)

Because the `.*` and `.?` matched characters including newlines (keep in mind that at the end of `Starting kernel...` there're `\n` characters)

It can be checked by looking at the `match.rm_so` and `match.rm_eo`.

`cbmem -c` showed whole log since the matching pattern is applied only `if (type != CONSOLE_PRINT_FULL)`.

For `cbmem -1`, the cursor position was set to the start of the second boot log (off by one `\n`), so we're fine (I believe no one noticed missing `\n` at the beginning of the boot log).

However, for the `cbmem -2`, we've hit:
```
        if (type == CONSOLE_PRINT_PREVIOUS) {
                console_c[cursor] = '\0';
                cursor = previous;
        }
```

where before this if statement, `cursor` was equal to `previous + 1`, so the next character in `console_c` buffer was NULL - that's why the `cbmem -2` was not working properly (due to `.?` in regex matched newlines).

Change from https://review.coreboot.org/c/coreboot/+/62720 introduced this issue (by switching to REG_EXTENDED syntax and using `.?`).
Prior to this CL, `cbmem -2` worked fine since only two (instead of three) matches occured (no `.?` in BANNER_REGEX).

`-- Long version ends here --`

Nevertheless, please correct me if I'm wrong here - I believe that the intention was to not catch newlines with particular regex (since regex itself contains escaped `\n` characters to be matched explicitly). Moreover, I believe that this code shall  match only the first line of boot log, not the whole boot log to `Starting kernel...`.

Adding REG_NEWLINE to `rexcomp` does exactly that (while keeping the loglevel markers support in place). If you think there's a better way to solve it, I'd be grateful to hear your ideas.