libfido2: Fix test for Linux

Fixes:
/home/linuxbrew/.linuxbrew/Cellar/libfido2/1.7.0/include/fido/types.h:54:9: error: unknown type name ‘sigset_t’
typedef sigset_t fido_sigset_t;

This type is not part of the c99 standard

Formula/libfido2.rb

@@ -47,7 +47,7 @@ class Libfido2 < Formula
       fido_dev_info_free(&devlist, max_devices);
     }
     EOF
-    system ENV.cc, "-std=c99", "test.c", "-I#{include}", "-I#{Formula["openssl@1.1"].include}", "-o", "test",
+    system ENV.cc, "test.c", "-I#{include}", "-I#{Formula["openssl@1.1"].include}", "-o", "test",
                    "-L#{lib}", "-lfido2"
     system "./test"
   end