Add read to buildtest and sys.h

sys.h

@@ -6,7 +6,15 @@ void exit(int8_t status);
 #define STDIO 1
 #define STDERR 2
 intptr_t write(int32_t fd, const void* buf, intptr_t size);
-//intptr_t read(int32_t fd, const void* buf, intptr_t size);
+#if defined(__x86_64__)
+intptr_t read(int32_t fd, const void* buf, intptr_t size);
+#endif
 
 uint32_t fork();
+
+// Provide memset for clang
+void *memset(void* s, int c, unsigned long n) {
+  int8_t* mem = s;
+  for(long int i = 0; i < n; ++i) mem[i] = c;
+}
 #endif // !MINIMALSYS_H