Compile for RISC-V.

Change-Id: I85f0364b83440469c0d15c32dd96607be31fc1b7
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/45904
Commit-Queue: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

include/openssl/base.h

@@ -105,6 +105,10 @@ extern "C" {
 #elif defined(__MIPSEL__) && defined(__LP64__)
 #define OPENSSL_64_BIT
 #define OPENSSL_MIPS64
+#elif defined(__riscv) && __SIZEOF_POINTER__ == 8
+#define OPENSSL_64_BIT
+#elif defined(__riscv) && __SIZEOF_POINTER__ == 4
+#define OPENSSL_32_BIT
 #elif defined(__pnacl__)
 #define OPENSSL_32_BIT
 #define OPENSSL_PNACL