Define CBS/CBB tags as uint32_t with a typedef.

We use unsigned, but we actually assume it is 32-bit for the bit-packing
strategy. But also introduce a typedef to hint that callers shouldn't
treat it as an arbitrary 32-bit integer. A typedef would also allow us
to extend to uint64_t in the future, if we ever need to.

Update-Note: Some APIs switch from unsigned * to uint32_t * out
pointers. This is only source-compatible if unsigned and uint32_t are
the exact same type. The CQ suggests this is indeed true. If they are
not, replace unsigned with CBS_ASN1_TAG to fix the build.

Bug: 525
Change-Id: I45cbe127c1aa252f5f6a169dca2e44d1e6e1d669
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/54986
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

include/openssl/base.h

diff --git a/include/openssl/base.h b/include/openssl/base.h
index 1e61e98..a2fb76b 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -335,6 +335,10 @@
 // are sizes of or indices into C objects, can be converted without overflow.
 typedef ptrdiff_t ossl_ssize_t;
 
+// CBS_ASN1_TAG is the type used by |CBS| and |CBB| for ASN.1 tags. See that
+// header for details. This type is defined in base.h as a forward declaration.
+typedef uint32_t CBS_ASN1_TAG;
+
 // CRYPTO_THREADID is a dummy value.
 typedef int CRYPTO_THREADID;