Add a missing ifdef to CRYPTO_set_fuzzer_mode call

Although the fuzzers are expected to be used with
FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION, build systems sometimes build
them in a non-fuzzer configuration. Keep the targets working in those
configs.

Change-Id: I351c3f6366ca97cb23144164fd5e49d1fa2286a6
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/78007
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Bob Beck <bbe@google.com>

fuzz/pkcs8.cc

diff --git a/fuzz/pkcs8.cc b/fuzz/pkcs8.cc
index 2d2181c..4aeaaa5 100644
--- a/fuzz/pkcs8.cc
+++ b/fuzz/pkcs8.cc
@@ -19,7 +19,9 @@
 #include <openssl/mem.h>
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
   CRYPTO_set_fuzzer_mode(1);
+#endif
 
   CBS cbs;
   CBS_init(&cbs, buf, len);