Add build test

buildtest.c

@@ -0,0 +1,48 @@
+#include <stdint.h>
+#include "sys.h"
+
+
+int main() {
+#if defined(__x86_64__) || defined(__aarch64__) || defined(__mips__)
+  uint64_t pid = fork();
+  char msg[17] = {' '};
+  msg[16] = '\n';
+  for(int i = 0; i < 16; ++i) {
+    char nibble = (pid >> ((15 - i) * 4)) & 0xf;
+    char c;
+    if (nibble > 9) {c = nibble + '7';}
+    else {c = nibble + '0';}
+    msg[i] = c;
+  }
+  write(STDIO, msg, 17);
+  #else
+  char *msg = "Hello World!\n";
+  write(STDIO, msg, 13);
+#endif
+  return 69;
+}
+void __libc_start_main() {exit(main());}
+
+void _start() {
+  __libc_start_main();
+}
+
+void __start() {
+  _start();
+}
+/*
+#if defined(__x86_64__)
+        printf("Compiled for x86_64 architecture\n");
+    #elif defined(__i386__)
+        printf("Compiled for x86 architecture\n");
+    #elif defined(__arm__)
+        printf("Compiled for ARM architecture\n");
+    #elif defined(__aarch64__)
+        printf("Compiled for ARM64 architecture\n");
+    #elif defined(__mips__)
+        printf("Compiled for ARM architecture\n");
+    #else
+        printf("Unknown architecture\n");
+    #endif
+*/
+