Turns out the cause of CodeQL hangs (or probably just extreme long
compile) is the header `curl/typecheck-gcc.h`. By accident I noticed
that the preprocessed output of libtests.c is 75 MB (megabytes). This
is much higher than the amounf of source code hinted, also compared to
e.g. units.c or other build targets. The reason for the extreme size
is each easy option call pulling in the large checker logic defined
in this header.

By compiling with `-DCURL_DISABLE_TYPECHECK`, preprocessed output drops
to 2.2 MB (34x), and the libtests target builds without issues.

Also build all tests and examples with the Linux HTTP/3 config, covering
3 more files.

With these, CodeQL C coverage is 893 out of 930 (96%) (was: 645 69%)

Follow-up to 71fc11e #18695
Follow-up to a333fd4 #18557
Follow-up to b4922b1 #18564

Closes vszakats#11
Closes #19632