Change noinline to dontinline (#312)

We defined `noinline` as an abbreviation for the longer version
`__attribute__((__noinline__))` which caused name clashes since
third party codebases often write it as `__attribute__((noinline))`.

libc/mem/arena.c

@@ -103,7 +103,7 @@ static size_t __arena_bulk_free(void *p[], size_t n) {
   return 0;
 }
 
-static noinline bool __arena_grow(size_t offset, size_t request) {
+static dontinline bool __arena_grow(size_t offset, size_t request) {
   size_t greed;
   greed = __arena.size + 1;
   do {