This patch broke bootstrap on AIX due to its use of strchrnul().  It is an
extension available in Linux, but not all targets.

/src/src/gcc/cp/contracts.cc:213:21: error: 'strchrnul' was not declared in
this scope; did you mean 'strchr'?
  213 |   size_t role_len = strchrnul (role, ':') - role;
      |                     ^~~~~~~~~
      |                     strchr

Would you please avoid the extension or provide an implementation?

Thanks David