tree-wide: Mark linux and sys includes as system includes

Even though these are in our tree, we should still treat them as
system includes which helps various tools (clangd, iwyu, ...) understand
that these are system includes and <> should be used instead of "".

src/basic/meson.build

@@ -133,14 +133,14 @@ generate_arphrd_list = find_program('generate-arphrd-list.sh')
 arphrd_list_txt = custom_target(
         'arphrd-list.txt',
         output : 'arphrd-list.txt',
-        command : [generate_arphrd_list, cpp, files('linux/if_arp.h'), config_h],
+        command : [generate_arphrd_list, cpp, files('include/linux/if_arp.h'), config_h],
         capture : true)
 
 generate_cap_list = find_program('generate-cap-list.sh')
 cap_list_txt = custom_target(
         'cap-list.txt',
         output : 'cap-list.txt',
-        command : [generate_cap_list, cpp, files('linux/capability.h')],
+        command : [generate_cap_list, cpp, files('include/linux/capability.h')],
         capture : true)
 
 generate_errno_list = find_program('generate-errno-list.sh')
@@ -238,7 +238,7 @@ run_target(
 ############################################################
 
 filesystem_includes = files(
-        'linux/magic.h',
+        'include/linux/magic.h',
         'missing_magic.h',
 )