deps: update fmt to latest version (#3403)

This updates `fmt` to the latest version and moves to just being a copy
of their repo to make updating easier (no editing their cmake / figuring
out which files to minimally include).

The motivation for this is now that we switched to C++ 20, there were a
ton of deprecated function usages that is going away in future compiler
versions. This gets rid of all those warnings.

decompiler/analysis/cfg_builder.cpp

@@ -4,7 +4,9 @@
  */
 
 #include "cfg_builder.h"
+
 #include "common/log/log.h"
+
 #include "decompiler/Function/Function.h"
 #include "decompiler/IR2/Form.h"
 #include "decompiler/ObjectFile/LinkedObjectFile.h"