Use C99 for size_t loops.

This was done just by grepping for 'size_t i;' and 'size_t j;'. I left
everything in crypto/x509 and friends alone.

There's some instances in gcm.c that are non-trivial and pulled into a
separate CL for ease of review.

Change-Id: I6515804e3097f7e90855f1e7610868ee87117223
Reviewed-on: https://boringssl-review.googlesource.com/10801
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/test/test_util.cc b/crypto/test/test_util.cc
index 8021aaa..928972a 100644
--- a/crypto/test/test_util.cc
+++ b/crypto/test/test_util.cc
@@ -20,10 +20,9 @@
 
 void hexdump(FILE *fp, const char *msg, const void *in, size_t len) {
   const uint8_t *data = reinterpret_cast<const uint8_t*>(in);
-  size_t i;
 
   fputs(msg, fp);
-  for (i = 0; i < len; i++) {
+  for (size_t i = 0; i < len; i++) {
     fprintf(fp, "%02x", data[i]);
   }
   fputs("\n", fp);