Prevent wineg++ from including the SAL headers

This otherwise breaks compilation under Wine 6.20:

https://bugs.winehq.org/show_bug.cgi?id=51919

CHANGELOG.md

@@ -15,6 +15,13 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   running the Wine process under a separate namespace. If you don't know that
   you need this, then you probably don't need this!
 
+### Changed
+
+- Added a workaround for a new
+  [bug](https://bugs.winehq.org/show_bug.cgi?id=51919) in Wine 6.20 that would
+  cause compilation to fail by redefining common variable names used in the
+  standard library.
+
 ### Fixed
 
 - The socket endpoint used by a plugin group host process to accept new

meson.build

@@ -69,6 +69,13 @@ wine_compiler_options = [
   #
   # https://bugs.winehq.org/show_bug.cgi?id=50670
   '-D__IFileOperation_INTERFACE_DEFINED__',
+  # This Wine 6.20 commit `dfdf56fbe47f8ff50ebe533e6d73f2de6546f008` added a
+  # bunch of new SAL includes to `windows.h`, which include things like `__in`
+  # and `__out`. This breaks libstdc++ compilation since they often use those
+  # names for function parameters.
+  #
+  # https://bugs.winehq.org/show_bug.cgi?id=51919
+  '-D__WINE_SAL_H__',
 ]
 
 # NOTE: GCC doesn't 8-byte align doubles in structs on x86 for ABI-compatibilty