hintSource wrong for stdinfile.nim stdin

[timotheecour]

• hintSource

echo 'import math; round(float(25) * 2.54, 2)' | ./bin/nim c -r -
stdinfile.nim(1, 14) Warning: use strformat module instead; round is deprecated [Deprecated]

               ^
stdinfile.nim(1, 19) Error: expression 'round(63.5, 2)' is of type 'float' and has to be discarded

                    ^

source should point to stdin input (serialized as string)

• similarly, stdin input should be used to tell whether to recompile in here fix #13412 nim now recompiles for stdin input; SuccessX now configurable; can show whether it recompiled nim-lang/Nim#13506