Define OPENSSL_64_BIT for PowerPC chips.

We had aarch64 handled twice, which was a mistake.

Change-Id: Id27fc86cb701a87c11c54b98534108f87e49262d
Reviewed-on: https://boringssl-review.googlesource.com/5131
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/base.h

@@ -79,9 +79,8 @@ extern "C" {
 #elif defined(__arm) || defined(__arm__) || defined(_M_ARM)
 #define OPENSSL_32_BIT
 #define OPENSSL_ARM
-#elif defined(__aarch64__)
+#elif defined(__PPC64__) || defined(__powerpc64__)
 #define OPENSSL_64_BIT
-#define OPENSSL_AARCH64
 #elif defined(__mips__) && !defined(__LP64__)
 #define OPENSSL_32_BIT
 #define OPENSSL_MIPS