build: remove fchmod() check

This is UNIX-only code, and this function has been in POSIX since
forever. Even Android has it. The test should be unnecessary, so remove
it.

input/ipc-unix.c

@@ -314,9 +314,7 @@ static void *ipc_thread(void *p)
         goto done;
     }
 
-#if HAVE_FCHMOD
     fchmod(ipc_fd, 0600);
-#endif
 
     size_t path_len = strlen(arg->path);
     if (path_len >= sizeof(ipc_un.sun_path) - 1) {

wscript

@@ -281,10 +281,6 @@ iconv support use --disable-iconv.",
         'desc': 'any glob() support',
         'deps': 'glob-posix || glob-win32',
         'func': check_true,
-    }, {
-        'name': 'fchmod',
-        'desc': 'fchmod()',
-        'func': check_statement('sys/stat.h', 'fchmod(0, 0)'),
     }, {
         'name': 'vt.h',
         'desc': 'vt.h',