Now that fmt plays nice with gcc let's actually use it: replace std::to_string, boost lexical_cast and a couple miscellaneous llformats with fmt. (Alchemy sync-ish)

indra/llcommon/llformat.h

@@ -34,6 +34,16 @@
 #ifndef LL_LLFORMAT_H
 #define LL_LLFORMAT_H
 
+#if defined(LL_CLANG)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated"
+#endif
+#include <fmt/format.h>
+#include <fmt/printf.h>
+#if defined(LL_CLANG)
+#pragma clang diagnostic pop
+#endif
+
 // Use as follows:
 // LL_INFOS() << llformat("Test:%d (%.2f %.2f)", idx, x, y) << LL_ENDL;
 //