Make more fixes and improvements

- Fix Makefile flaking due to ZIPOBJ_FLAGS generation
- Make printf() floating point and gdtoa thread safe
- Polish up the runit / runitd programs some more
- Prune some more makefile dependencies

libc/stdio/getc.c

@@ -24,5 +24,5 @@
  * @threadsafe
  */
 int(getc)(FILE *f) {
-  return getc(f);
+  return fgetc(f);
 }