Add ktx

ktx/external/fmt/test/header-only-test.cc

@@ -0,0 +1,11 @@
+// Header-only configuration test
+
+#include "fmt/base.h"
+#include "fmt/ostream.h"
+#include "gtest/gtest.h"
+
+#ifndef FMT_HEADER_ONLY
+#  error "Not in the header-only mode."
+#endif
+
+TEST(header_only_test, format) { EXPECT_EQ(fmt::format("foo"), "foo"); }