Warnings are not aloud if you want to build correctly nginx

[concatime]

Hi.
When using the recommended -Wformat -Werror=format-security, it's impossible to build because of these warnings:

src/core/ngx_string.c:2040:9: error: assigning to 'u_char *' (aka 'unsigned char *') from 'char [24]' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
        prefix = NGX_PREFIX;
               ^ ~~~~~~~~~~
src/core/ngx_string.c:2042:23: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
    if (prefix[strlen(prefix) - 1] == '/')
                      ^~~~~~
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2043:16: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
        plen = strlen(prefix) - 1;
                      ^~~~~~
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2045:16: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
        plen = strlen(prefix);
                      ^~~~~~
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2047:49: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
    if (!ngx_strncmp(path->data, prefix, strlen(prefix))) {
                                                ^~~~~~
src/core/ngx_string.h:53:79: note: expanded from macro 'ngx_strncmp'
#define ngx_strncmp(s1, s2, n)  strncmp((const char *) s1, (const char *) s2, n)
                                                                              ^
/usr/include/x86_64-linux-gnu/bits/string2.h:154:41: note: expanded from macro 'strncmp'
  (__extension__ (__builtin_constant_p (n)                                    \
                                        ^
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2047:49: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
    if (!ngx_strncmp(path->data, prefix, strlen(prefix))) {
                                                ^~~~~~
src/core/ngx_string.h:53:79: note: expanded from macro 'ngx_strncmp'
#define ngx_strncmp(s1, s2, n)  strncmp((const char *) s1, (const char *) s2, n)
                                                                              ^
/usr/include/x86_64-linux-gnu/bits/string2.h:156:38: note: expanded from macro 'strncmp'
                       && strlen (s1) < ((size_t) (n)))                       \
                                                   ^
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2047:49: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
    if (!ngx_strncmp(path->data, prefix, strlen(prefix))) {
                                                ^~~~~~
src/core/ngx_string.h:53:79: note: expanded from macro 'ngx_strncmp'
#define ngx_strncmp(s1, s2, n)  strncmp((const char *) s1, (const char *) s2, n)
                                                                              ^
/usr/include/x86_64-linux-gnu/bits/string2.h:158:34: note: expanded from macro 'strncmp'
                          && strlen (s2) < ((size_t) (n))))                   \
                                                      ^
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2047:49: error: passing 'u_char *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
    if (!ngx_strncmp(path->data, prefix, strlen(prefix))) {
                                                ^~~~~~
src/core/ngx_string.h:53:79: note: expanded from macro 'ngx_strncmp'
#define ngx_strncmp(s1, s2, n)  strncmp((const char *) s1, (const char *) s2, n)
                                                                              ^
/usr/include/x86_64-linux-gnu/bits/string2.h:159:42: note: expanded from macro 'strncmp'
                  ? strcmp (s1, s2) : strncmp (s1, s2, n)))
                                                       ^
/usr/include/string.h:394:35: note: passing argument to parameter '__s' here
extern size_t strlen (const char *__s)
                                  ^
src/core/ngx_string.c:2049:24: error: passing 'char *' to parameter of type 'u_char *' (aka 'unsigned char *') converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
       x = ngx_cpystrn(buf, path->data + plen, path->len);
                       ^~~
src/core/ngx_string.c:49:21: note: passing argument to parameter 'dst' here
ngx_cpystrn(u_char *dst, u_char *src, size_t n)
                    ^
src/core/ngx_string.c:2049:10: error: assigning to 'char *' from 'u_char *' (aka 'unsigned char *') converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
       x = ngx_cpystrn(buf, path->data + plen, path->len);
         ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/core/ngx_string.c:2051:19: error: assigning to 'u_char *' (aka 'unsigned char *') from 'char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
       path->data = buf;
                  ^ ~~~
11 errors generated.
make[1]: *** [objs/src/core/ngx_string.o] Error 1
make: *** [build] Error 2

It would be paradoxal/ironic to not use the recommended habits in a patch coming from OpenBSD, known for its security ;)