Fix build of www/squid and www/squid-devel with clang 8
This fixes an error with a defaulted copy constructor:
../../src/security/ServerOptions.h:38:5: error: explicitly defaulted copy constructor is implicitly deleted [-Werror,-Wdefaulted-function-deleted]
ServerOptions(const ServerOptions &) = default;
^
../../src/security/ServerOptions.h:110:29: note: copy constructor of 'ServerOptions' is implicitly deleted because field 'clientCaStack' has a deleted copy constructor
X509_NAME_STACK_Pointer clientCaStack;
^
/usr/include/c++/v1/memory:2494:3: note: copy constructor is implicitly deleted because 'unique_ptr<stack_st_X509_NAME, Security::ServerOptions::sk_X509_NAME_free_wrapper>' has a user-declared move constructor
unique_ptr(unique_ptr&& __u) noexcept
^
The copy constructor can instead be deleted.
Approved by: portmgr (joneum)
PR: 236210
bef1ed3bc3