## Problem
In the case of an existing `fmt` namespace (in my project this looks like `Project::fmt`) it is possible to get a namespace clash in debug builds (MSVC 2017)
## Proposed Solution
When referencing `fmt` internally, be explicit that it is relative to the global namespace using `::fmt`
The nvcc compiler (at least up to 9.2) defines `__SIZEOF_INT128__`, but doesn't support 128-bit integers on device code:
```
error: "fmt::v6::format_arg_store<fmt::v6::basic_format_context<std::back_insert_iterator<fmt::v6::internal::buffer<char>>, char>, const char *, int, const char *>" contains a 128-bit integer, which is not supported in device code
```
The `std::is_base_of<T,U>()` and `std::is_reference<T>()` member functions were added in C++14. To maintain C++11 compatibility, use the `::value` instead.
Current code fails on intel-17 and other compilers if using strict C++11
The intel-17 and intel-18 compilers seem to require that `u` be `const`:
```
/src/fmt/format.h(226): warning #437: reference to local variable of enclosing function is not allowed
char data[sizeof(u)];
```
If `u` is declared as `const auto u =1u` instead of just `auto u=1u`, the file compiles with no warnings.
Otherwise, Google Test will insist on inserting 'char8_t' NTBS into 'char' streams, but basic_ostream<char>::operator<< overloads taking 'char8_t' arguments are defined as deleted by P1423.
Handling individual 'char8_t's is done inline.
This fixes the compilation errors seen in C++20 mode beginning with VS2019 Update 2.
Signed-off-by: Daniela Engert <dani@ngrt.de>
