include: move libc header wrappers to src/include/override/, and kernel headers to src/include/uapi/

Preparation for later changes.

man/meson.build

@@ -38,7 +38,7 @@ man_page_depends += custom_entities_ent
 generate_bpf_delegate_configs = find_program('../src/basic/generate-bpf-delegate-configs.py')
 
 bpf_delegate_xml = custom_target(
-        input : files('../src/basic/include/linux/bpf.h'),
+        input : files('../src/include/uapi/linux/bpf.h'),
         output : 'bpf-delegate.xml',
         command : [generate_bpf_delegate_configs,
                    'doc',

meson.build

@@ -2008,16 +2008,25 @@ dbus_programs = []
 # A list of boot stubs. Required for testing of ukify.
 boot_stubs = []
 
+system_includes = [
+        include_directories(
+                # gcc(1) says
+                # "Directories specified with -isystem options are scanned in left-to-right order",
+                # and meson puts the directories in the reversed order. Hence, a directory with a lower
+                # priority must be listed earlier.
+                'src/include/uapi',
+                'src/include/override',
+                is_system : true,
+        ),
+]
+
 basic_includes = [
         include_directories(
                 'src/basic',
                 'src/fundamental',
                 'src/systemd',
         ),
-        include_directories(
-                'src/basic/include',
-                is_system : true,
-        ),
+        system_includes,
         version_include,
 ]
 

src/basic/meson.build

@@ -127,19 +127,19 @@ basic_sources += missing_syscall_def_h
 generate_af_list = find_program('generate-af-list.sh')
 af_list_txt = custom_target(
         output : 'af-list.txt',
-        command : [generate_af_list, cpp, files('include/sys/socket.h')],
+        command : [generate_af_list, cpp, files('../include/override/sys/socket.h')],
         capture : true)
 
 generate_arphrd_list = find_program('generate-arphrd-list.sh')
 arphrd_list_txt = custom_target(
         output : 'arphrd-list.txt',
-        command : [generate_arphrd_list, cpp, files('include/linux/if_arp.h')],
+        command : [generate_arphrd_list, cpp, files('../include/uapi/linux/if_arp.h')],
         capture : true)
 
 generate_cap_list = find_program('generate-cap-list.sh')
 cap_list_txt = custom_target(
         output : 'cap-list.txt',
-        command : [generate_cap_list, cpp, files('include/linux/capability.h')],
+        command : [generate_cap_list, cpp, files('../include/uapi/linux/capability.h')],
         capture : true)
 
 generate_errno_list = find_program('generate-errno-list.sh')
@@ -234,7 +234,7 @@ run_target(
 ############################################################
 
 filesystem_includes = files(
-        'include/linux/magic.h',
+        '../include/uapi/linux/magic.h',
         'missing_magic.h',
 )
 
@@ -275,7 +275,7 @@ filesystem_switch_case_inc = custom_target(
 
 generate_bpf_delegate_configs = find_program('generate-bpf-delegate-configs.py')
 bpf_delegate_configs_inc = custom_target(
-        input : files('include/linux/bpf.h'),
+        input : files('../include/uapi/linux/bpf.h'),
         output : 'bpf-delegate-configs.inc',
         command : [generate_bpf_delegate_configs,
                    'code',