Allows win32_main() to throw exceptions.

A few exceptions are needed for sources which include COM header
(directly or indirectly).

This fixes lots of shadow warnings, see
https://github.com/MusicPlayerDaemon/MPD/issues/1150

Include the most specific header documented by MSDN instead.

MSDN documentation suggests always passing this flag to reduce
overhead for an "obsolete technology".

None of the current FormatHResultError() callers need the format string.

Parameters should better be captured.  This removes some complexity
from Async().

Reduce header dependencies.

Reduce header dependencies.

Fixes linker failure on test/run_output.exe

Casting to std::runtime_error loses information (and prevents RVO).

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.