main: require argv[0]

sure, linux has been providing argv[0] by default for a while now. other
OSes may not be as forthcoming though, and relying on the OS to create a
world in which we can just make assumptions we could test for instead is
unnecessarily lazy. we *could* default argv0, but that's a little silly.

notably we abort instead of returning normally to avoid confusions where
a caller interprets our exit status like a Worker build results bitmask.

Change-Id: Id73f8cd0a630293b789c59a8c4b0c4a2b936b505

src/nix/main.cc

@@ -503,6 +503,11 @@ void mainWrapped(int argc, char * * argv)
 
 int main(int argc, char * * argv)
 {
+    if (argc < 1) {
+        std::cerr << "no, we don't have pkexec at home. provide argv[0]." << std::endl;
+        std::abort();
+    }
+
     // Increase the default stack size for the evaluator and for
     // libstdc++'s std::regex.
     nix::setStackSize(64 * 1024 * 1024);