Do not include <Security/cssm.h> on iOS as it does not exist.

crypto/signature_creator.h

Index: crypto/signature_creator.h
diff --git a/crypto/signature_creator.h b/crypto/signature_creator.h
index 8d25c4dada2979e403625963b84ead9d12595d4a..301ab19bc1acbead6716be33f8a6d53b15964cc6 100644
--- a/crypto/signature_creator.h
+++ b/crypto/signature_creator.h
@@ -13,7 +13,7 @@ typedef struct env_md_ctx_st EVP_MD_CTX;
 #elif defined(USE_NSS)
 // Forward declaration.
 struct SGNContextStr;
-#elif defined(OS_MACOSX)
+#elif defined(OS_MACOSX) && !defined(OS_IOS)
 #include <Security/cssm.h>
 #endif
 
@@ -56,7 +56,7 @@ class CRYPTO_EXPORT SignatureCreator {
   EVP_MD_CTX* sign_context_;
 #elif defined(USE_NSS)
   SGNContextStr* sign_context_;
-#elif defined(OS_MACOSX)
+#elif defined(OS_MACOSX) && !defined(OS_IOS)
   CSSM_CC_HANDLE sig_handle_;
 #elif defined(OS_WIN)
   ScopedHCRYPTHASH hash_object_;