Add x86_64 start code to access argc and argv

buildtest.c

@@ -2,11 +2,18 @@
 #include "sys.h"
 
 
-int main() {
+int main(int argc, char* argv[]) {
   // Test the write syscall
   intptr_t n = write(STDOUT, "Hello\n", 6);
   if(n != 6) return n;
 
+  // Test argc
+  for(int i = 0; i < argc; ++i){
+    int len = strlen(argv[i]);
+    write(STDOUT, argv[i], len);
+    write(STDOUT, "\n", 1);
+  }
+
   // Test the fork syscall
   uint64_t pid = fork();
   // Print the pid in hex