Fix more Visual Studio 2019 pedantic warnings (#1371)

* format-inl.h(444,1): warning C4804: '>>': unsafe use of type 'bool' in operation
format.h(2808,1): warning C4127: conditional expression is constant

* More fixes for VS2019 pedantic warnings

* Fix "conditional expression is constant" VS2019 warning in more specific way

* Use const_check to silence constexpr warning

include/fmt/printf.h

@@ -16,10 +16,6 @@
 FMT_BEGIN_NAMESPACE
 namespace internal {
 
-// A helper function to suppress bogus "conditional expression is constant"
-// warnings.
-template <typename T> inline T const_check(T value) { return value; }
-
 // Checks if a value fits in int - used to avoid warnings about comparing
 // signed and unsigned integers.
 template <bool IsSigned> struct int_checker {