In an attempt to upgrade from 12-stable amd64 system to 14-stable, I've got new sources via git, just like it is said in the Handbook.
But the `make buildworld` command fails with these errors:

--- all_subdir_usr.sbin/jail ---
/usr/src/usr.sbin/jail/jaillex.l:106:6: error: comparison of integers of different signs: 'int' and 'yy_size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
                                        yyless(atvar);
                                        ^~~~~~~~~~~~~
jaillex.c:215:9: note: expanded from macro 'yyless'
        YY_LESS_LINENO(yyless_macro_arg);\
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
jaillex.c:204:36: note: expanded from macro 'YY_LESS_LINENO'
                for ( yyl = n; yyl < yyleng; ++yyl )\
                               ~~~ ^ ~~~~~~
/usr/src/usr.sbin/jail/jaillex.l:146:5: error: comparison of integers of different signs: 'int' and 'yy_size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
                                yyless(0);
                                ^~~~~~~~~
jaillex.c:215:9: note: expanded from macro 'yyless'
        YY_LESS_LINENO(yyless_macro_arg);\
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
jaillex.c:204:36: note: expanded from macro 'YY_LESS_LINENO'
                for ( yyl = n; yyl < yyleng; ++yyl )\
                               ~~~ ^ ~~~~~~
jaillex.c:1906:58: error: unused parameter 'yyscanner' [-Werror,-Wunused-parameter]
static void yy_fatal_error (yyconst char* msg , yyscan_t yyscanner)
                                                         ^
jaillex.c:2226:43: error: unused parameter 'yyscanner' [-Werror,-Wunused-parameter]
void *yyalloc (yy_size_t  size , yyscan_t yyscanner)
                                          ^
jaillex.c:2231:58: error: unused parameter 'yyscanner' [-Werror,-Wunused-parameter]
void *yyrealloc  (void * ptr, yy_size_t  size , yyscan_t yyscanner)
                                                         ^
jaillex.c:2243:36: error: unused parameter 'yyscanner' [-Werror,-Wunused-parameter]
void yyfree (void * ptr , yyscan_t yyscanner)
                                   ^
6 errors generated.
*** [jaillex.o] Error code 1

make[4]: stopped in /usr/src/usr.sbin/jail
--- all_subdir_usr.bin ---
--- all_subdir_usr.bin/lex ---
--- all_subdir_usr.bin/clang ---
--- all_subdir_tests ---
--- all_subdir_usr.bin ---
--- all_subdir_usr.bin/kyua ---
--- all_subdir_lib ---


------------
Apart from that I get a bunch of warnings like these, but I suppose it should not stop the world from building:

__cxa_thread_call_dtors: dtr 0xc34b10 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xc35190 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xc354c0 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xbc35f0 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xc35190 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xc354c0 from unloaded dso, skipping
__cxa_thread_call_dtors: dtr 0xc34b10 from unloaded dso, skipping

-----------