OpenBSD Support

Includes bits by me and Robert Nagy <robert.nagy@gmail.com> who has a
google CLA.

Update-Note: Additionally, BoringSSL now requires macOS 10.12 or later
for getentropy support. This is consistent with
https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md

WANT_LGTM=all

Change-Id: I5ab74fa8a6677fac29c316aa29a954df401ba647
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/59225
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/base.h

diff --git a/include/openssl/base.h b/include/openssl/base.h
index 67429c0..3141676 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -164,6 +164,10 @@
 #define OPENSSL_FREEBSD
 #endif
 
+#if defined(__OpenBSD__)
+#define OPENSSL_OPENBSD
+#endif
+
 // BoringSSL requires platform's locking APIs to make internal global state
 // thread-safe, including the PRNG. On some single-threaded embedded platforms,
 // locking APIs may not exist, so this dependency may be disabled with the

include/openssl/thread.h

diff --git a/include/openssl/thread.h b/include/openssl/thread.h
index c6e357e..afa9f08 100644
--- a/include/openssl/thread.h
+++ b/include/openssl/thread.h
@@ -78,6 +78,10 @@
   void *handle;
 } CRYPTO_MUTEX;
 #elif !defined(__GLIBC__)
+#if defined(OPENSSL_OPENBSD)
+// OpenBSD does not guarantee pthread_rwlock_t in sys/types.h yet.
+#include <pthread.h>
+#endif
 typedef pthread_rwlock_t CRYPTO_MUTEX;
 #else
 // On glibc, |pthread_rwlock_t| is hidden under feature flags, and we can't