unzip: fix build GCC 15.1

unzip: fix build GCC 15.1

refer to:

https://gitlab.alpinelinux.org/alpine/aports/-/blob/b7410ac718d5eeae21001de5cae9159f597bb517/main/unzip/gcc15.patch

fix this:

unix/unxcfg.h:120:15: error: conflicting types for 'gmtime'; have 'struct tm *(void)'
  120 |    struct tm *gmtime(), *localtime();
      |               ^~~~~~
In file included from unix/unxcfg.h:119:
/home/nasbdh9/openwrt/staging_dir/toolchain-x86_64_gcc-15.1.0_musl/include/time.h:59:12: note: previous declaration of 'gmtime' with type 'struct tm *(const time_t *)' {aka 'struct tm *(const long int *)'}
   59 | struct tm *gmtime (const time_t *);
      |            ^~~~~~
unix/unxcfg.h:120:26: error: conflicting types for 'localtime'; have 'struct tm *(void)'
  120 |    struct tm *gmtime(), *localtime();
      |                          ^~~~~~~~~
/home/nasbdh9/openwrt/staging_dir/toolchain-x86_64_gcc-15.1.0_musl/include/time.h:60:12: note: previous declaration of 'localtime' with type 'struct tm *(const time_t *)' {aka 'struct tm *(const long int *)'}
   60 | struct tm *localtime (const time_t *);
      |            ^~~~~~~~~

Signed-off-by: Tan Zien <[email protected]>