Make use of modern standard types

Summary: stdint.h defines the modern standard c types which have a fixed memory size. This makes the program run more predictably as well as removing the need to ugly double work types such as `unsigned int` or `long long`.

Reviewed By: lucasr

Differential Revision: D3649096

fbshipit-source-id: dc9fc8861c3106494c5d00d6ac337da50a4c945b

benchmarks/CSSBenchmark.c

@@ -18,7 +18,7 @@ CSS_BENCHMARKS({
     CSSNodeStyleSetWidth(root, 100);
     CSSNodeStyleSetHeight(root, 100);
 
-    for (int i = 0; i < 3; i++) {
+    for (uint32_t i = 0; i < 3; i++) {
       CSSNodeRef child = CSSNodeNew();
       CSSNodeStyleSetHeight(child, 20);
       CSSNodeStyleSetFlex(child, 1);