meson: Rework clang-tidy integration to be done via unit tests

Instead of using run-clang-tidy.py with its own scheduling, let's
just gather a list of source files ourselves and then use that to
add a unit test for each source file that runs clang-tidy on the
source file.

We also add a bit of logic to run clang-tidy on most header files
as well for extra coverage. This uncovered various header files that
were not standalone so this commit also includes fixes to make sure
the clang-tidy tests are all green.

We can also use this in a later commit to run clang-include-cleaner
on each source file in the same way.

src/shared/meson.build

@@ -317,6 +317,7 @@ ethtool_link_mode_h = custom_target(
 
 generated_sources += ethtool_link_mode_h
 shared_sources += ethtool_link_mode_h
+sources += shared_sources
 
 fname = 'ethtool-link-mode.xml'
 ethtool_link_mode_xml = custom_target(

src/shared/smack-util.h

@@ -7,6 +7,7 @@
   Author: Auke Kok <auke-jan.h.kok@intel.com>
 ***/
 
+#include <errno.h>
 #include <stdbool.h>
 #include <sys/types.h>
 

src/shared/utmp-wtmp.h

@@ -4,6 +4,7 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
+#include "assert-util.h"
 #include "time-util.h"
 
 #if ENABLE_UTMP