3da95ab2 breaks compilation on HP-UX with aCC

When compiling 9.11.6 on HP-UX 11.31 with aCC: HP C/aC++ B3910B A.06.29 [Oct 18 2016] I receive the following compilation errors in socket.c:

"socket.c", line 1619: warning #2223-D: function "typeof" declared implicitly
                        INSIST(msg->msg_controllen <= SENDCMSGBUFLEN);
                        ^

"socket.c", line 1619: error #2109: expression preceding parentheses of
          apparent call must have (pointer-to-) function type
                        INSIST(msg->msg_controllen <= SENDCMSGBUFLEN);

This is caused by 3da95ab2 which is according to this another annoying GNU extension. Please make this conditional on affected platforms/compilers only. As soon as I remove this from the BUFLEN defines the code compiles flawlessly.