Set trigger vector in whole words (#5857)

Having many triggers still hits a bottleneck in LLVM leading to long
compile times.

Instead of setting triggers bit-wise, set them as a whole 64-bit word
when possible. This improves C++ compile times by ~4x on some large
designs and has minor run-time performance benefit.

src/V3AstNodes.cpp

@@ -3018,7 +3018,8 @@ void AstCMethodHard::setPurity() {
                                                           {"resume", false},
                                                           {"reverse", false},
                                                           {"rsort", false},
-                                                          {"set", false},
+                                                          {"setBit", false},
+                                                          {"setWord", false},
                                                           {"set_randmode", false},
                                                           {"shuffle", false},
                                                           {"size", true},