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/boot/meson.build

@@ -348,6 +348,11 @@ if host_machine.cpu_family() in ['aarch64', 'arm', 'x86_64', 'x86']
         systemd_boot_sources += files('bcd.c')
 endif
 
+sources += libefi_sources
+sources += systemd_boot_sources
+sources += stub_sources
+sources += addon_sources
+
 boot_targets = []
 efi_elf_binaries = []
 efi_archspecs = [