Add support for Fuchsia in crypto/rand.

This change adds the OS-specific routines to get random bytes when using
BoringSSL on Fuchsia.  Fuchsia uses the Magenta kernel, which provides
random bytes via a syscall rather than via a file or library function.

Change-Id: I32f858246425309d643d142214c7b8de0c62250a
Reviewed-on: https://boringssl-review.googlesource.com/13140
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/include/openssl/base.h b/include/openssl/base.h
index 8c1fd34..3f47521 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -118,6 +118,10 @@
 #define OPENSSL_LINUX
 #endif
 
+#if defined(__Fuchsia__)
+#define OPENSSL_FUCHSIA
+#endif
+
 #if defined(TRUSTY)
 #define OPENSSL_TRUSTY
 #define OPENSSL_NO_THREADS