irc/quirc: unbreak with libc++ 3.9

servertcl.cc:890:12: error: assigning to 'char *' from incompatible type 'const char *'

while((pos=strstr(afterslash,"/"))) afterslash=pos+1;;
          ^~~~~~~~~~~~~~~~~~~~~~~

servertcl.cc:1010:12: error: assigning to 'char *' from incompatible type 'const char *'

while((pos=strstr(afterslash,"/"))) afterslash=pos+1;;
          ^~~~~~~~~~~~~~~~~~~~~~~

Reported by: pkg-fallout