coverity: fix multiple source code parse errors

Coverity scans the source code for static analysis, but its parser
has a couple of flaws...
The most common one is the failure to parse deprecation macros in
enum definitions, like:

```
  G_PARAM_PRIVATE GLIB_DEPRECATED_ENUMERATOR_IN_2_26 = G_PARAM_STATIC_NAME,
                  ^
  SD_JOURNAL_SYSTEM_ONLY _sd_deprecated_ = SD_JOURNAL_SYSTEM /* old name */
                         ^
```

but also recent gcc built-in macros, like:

```
  #if __has_builtin(__builtin_is_constant_evaluated)
      ^
  #if _GLIBCXX_HAS_BUILTIN(__has_unique_object_representations)
      ^
```

The solution is to replace the code with regular expressions at an earlier
stage. This can be configured directly in coverity with cov-configure