Introduce libc/mem/tinymalloc.inc

This allocator shaves ~20kb off single-threaded tool programs and is
slightly faster than proper malloc for simple non-demanding programs

tool/build/fixupobj.c

@@ -67,6 +67,8 @@ static Elf64_Ehdr *elf;
 static const char *epath;
 static Elf64_Xword symcount;
 
+#include "libc/mem/tinymalloc.inc"
+
 static wontreturn void Die(const char *reason) {
   tinyprint(2, epath, ": ", reason, "\n", NULL);
   exit(1);