Godbolt.org : Some Compilers throw a tantrum because they doesn't include standard library file by default

[Remi123]

AVR 4.6.4
AVR 5.4.0
WebAssembly clang

Solution : Predeclare std ratio content if is not found

Error Message :
https://raw.githubusercontent.com/Remi123/type_expr/master/include/type_expr.hpp:9:10: fatal error: 'ratio' file not found
#include
^~~~~~~
1 error generated.
Compiler returned: 1