Currently things work due to transitiveness, but we better not rely on that

From /usr/include/c++/10/cerrno:
This is a Standard C++ Library file. You should #include this file
in your programs, rather than any of the *.h implementation files.

This change was requested by Allen to fix things on Windows.
But saving all source code as utf8 makes very much sense anyway,
everywhere.

Setting this is about to be deprecated.

Also it causes a delay of 400ms before the runner gets queried,
this is noticeable when the results are displayed. Because there are no
serious performance issues in the search we can just remove the method
call.

GIT_SILENT: add sanitizers.supp so we can suppress some leak generated by some lib (as libfontconfig)

Currently we do word split by underscore. Th result is, that we
cannot search for anything with a underscore. To fix this we
need to add more words to the term list where also the term with
underscore is added. I search in the history of baloo: This handmade
term splitter was added to search for files with underscores (#336034).

So we need either get control over the term splitting, while searching,
or add the term with underscore to terms list. When we want to provide
both (splitted and non-splitted) we also need to take care about the
position parameter.

Without patching xapiantermgenerator we can sill search for the complete
email address on the commandline:

```
cd /tmp/searchplugintest/contacts
$ xapian-delve -t blue -d .
Posting List for term 'blue' (termfreq 1, collfreq 1, wdf_max 1): 101 []
$ xapian-delve -t jack_blue@test.com -d .
Posting List for term 'jack_blue@test.com' (termfreq 1, collfreq 1,
wdf_max 1): 101 []
```
but NOT:

```
$ xapian-delve -t jack_blue -d .
term 'jack_blue' not in database
```

FIXES: 370385
FIXED-IN: 5.17.0

CCBUG: 370385

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