Introduce `FMT_BEGIN_DETAIL_NAMESPACE` and `FMT_END_DETAIL_NAMESPACE` for `namespace detail` sections embedded in that part of the code that contains all declarations that are exported from the module, i.e. which is enclosed by `FMT_MODULE_EXPORT_BEGIN` and `FMT_MODULE_EXPORT_END`. Given a correct implementation of C++20 modules, neither the name `fmt::detail` nor any of its contents will become visible outside of the module.
* add FMT_INSTANTIATION_DEF_API for msvc
This should fix https://github.com/fmtlib/fmt/issues/2228
To fix difference dllexport requirements
msvc: dllexport at template instantiation definition in format.cc
clang: dllexport at template instantiation declaration (extern template) in format.h
If the ``_POSIX_`` flag is set, _fdopen will not be defined by
Mingw headers, which is addressed by this commit.
For what is worth, as opposed to ``fdopen``, ``_pipe`` *will*
actually have the ``_`` prefix when ``_POSIX_`` is set.
Make FMT_API symbols use the default visibility on non-Windows
platforms. Otherwise, one cannot use the generated fmt library when
compiling globally with -fvisibility=hidden.
Fixes compile errors like:
```
../3rdParty/fmt/include/fmt/core.h:757: error: undefined reference to 'fmt::v6::internal::assert_fail(char const*, int, char const*)'
```
Note that the symbol exists, but is local:
```
$ nm -C libfmtd.so.6.1.3 | grep assert_fail
U __assert_fail
0000000000233ffa t fmt::v6::internal::assert_fail(char const*, int, char const*)
```
With this patch, the compile error is gone and the symbol is properly
exported:
```
$ nm -a bin/libfmtd.so -C | grep assert_fail
U __assert_fail
00000000002366ba T fmt::v6::internal::assert_fail(char const*, int, char const*)
```
Change-Id: I96054e622d9a2ae81907e1b01a1033e629767a91
