Work around silly Win defines to support BoringSSL (#1148)

* Work around silly Win defines to support BoringSSL

* changes wrapped into ifdef(_WIN32) just in case

httplib.h

@@ -217,6 +217,14 @@ using socket_t = int;
 #include <thread>
 
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
+// these are defined in wincrypt.h and it breaks compilation if BoringSSL is used
+#if defined(_WIN32)
+#undef X509_NAME
+#undef X509_CERT_PAIR
+#undef X509_EXTENSIONS
+#undef PKCS7_SIGNER_INFO
+#endif
+
 #include <openssl/err.h>
 #include <openssl/md5.h>
 #include <openssl/ssl.h>