Return more placeholder version strings.

PyOpenSSL's tests expect all of the outputs to be distinct. OpenSSL also
tends to prefix the return values with strings like "compiler:", so do
something similar.

Change-Id: Ic411c95a276b477641ebad803ac309b3035c1b13
Reviewed-on: https://boringssl-review.googlesource.com/28544
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/crypto.c b/crypto/crypto.c
index 8ee4c82..f3ea9f7 100644
--- a/crypto/crypto.c
+++ b/crypto/crypto.c
@@ -167,10 +167,20 @@
 const char *SSLeay_version(int which) { return OpenSSL_version(which); }
 
 const char *OpenSSL_version(int which) {
-  if (which == OPENSSL_VERSION) {
-    return "BoringSSL";
+  switch (which) {
+    case OPENSSL_VERSION:
+      return "BoringSSL";
+    case OPENSSL_CFLAGS:
+      return "compiler: n/a";
+    case OPENSSL_BUILT_ON:
+      return "built on: n/a";
+    case OPENSSL_PLATFORM:
+      return "platform: n/a";
+    case OPENSSL_DIR:
+      return "OPENSSLDIR: n/a";
+    default:
+      return "not available";
   }
-  return "";
 }
 
 unsigned long SSLeay(void) { return OPENSSL_VERSION_NUMBER; }
diff --git a/include/openssl/crypto.h b/include/openssl/crypto.h
index 6678f2a..8e1a271 100644
--- a/include/openssl/crypto.h
+++ b/include/openssl/crypto.h
@@ -76,7 +76,8 @@
 #define OPENSSL_DIR 4
 
 // OpenSSL_version is a compatibility function that returns the string
-// "BoringSSL" if |which| is |OPENSSL_VERSION| and "" otherwise.
+// "BoringSSL" if |which| is |OPENSSL_VERSION| and placeholder strings
+// otherwise.
 OPENSSL_EXPORT const char *OpenSSL_version(int which);
 
 #define SSLEAY_VERSION OPENSSL_VERSION