Some fixes for MinGW

* Rename Windows.h uses to windows.h
  * Comment out structured exception handling usage

Makes MinGW happier. Mostly the same as previous work by
Nicolas Dufresne <nicolas.dufresne@collabora.com>, with the exception
that we now don't try to invoke RaiseException which would fail in MinGW
as it raises a Windows structured exception.

meson.build

@@ -105,6 +105,8 @@ elif host_system == 'linux'
   have_posix = true
 elif host_system == 'windows'
   platform_cflags += ['-DWEBRTC_WIN', '-D_WIN32', '-U__STRICT_ANSI__']
+  # this one is for MinGW to get format specifiers from inttypes.h in C++
+  platform_cflags += ['-D__STDC_FORMAT_MACROS=1']
   os_deps += [cc.find_library('winmm')]
   have_win = true
 endif