Add back __cdecl on older Wine versions

CHANGELOG.md

@@ -13,7 +13,9 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Changed part of the build process considering [this Wine
   bug](https://bugs.winehq.org/show_bug.cgi?id=49138). Building with Wine 5.7
   and 5.8 required a change, but that change now breaks builds using Wine 6.0
-  and up, so this change has been reverted.
+  and up. We now detect which version of Wine is used to build with, and we then
+  apply the change conditionally to be able to support building with both older
+  and newer versions of Wine.
 
 ## [2.2.1] - 2020-12-12
 

meson.build

@@ -48,6 +48,20 @@ if with_winedbg
   compiler_options += '-DWITH_WINEDBG'
 endif
 
+# Wine versions after Wine 5.6 and before 6.0 require a `__cdecl` calling
+# convention to be specified on the `main()` functions or else `argc` and `argv`
+# will point to the wrong memory. Similarly, with other versions of Wine this
+# should _not_ be specified for the same reason. We'll try to figure out the
+# current Wine version and add this calling convention based on that.
+#
+# https://bugs.winehq.org/show_bug.cgi?id=49138
+wine_version = run_command('sh', '-c', '''wine --version | grep --only-matching -E '[0-9]+\.[0-9.]+' | head -n1''')
+if wine_version.returncode() == 0 and \
+   wine_version.stdout().version_compare('>=5.7') and \
+   wine_version.stdout().version_compare('<6.0')
+  compiler_options += '-DWINE_USE_CDECL'
+endif
+
 # Generate header files for configuration variables such as the current git tag
 # and the name of the host binary
 subdir('src/common/config')

src/wine-host/group-host.cpp

@@ -36,7 +36,11 @@
  * this group plugin host will function identically on both the plugin and the
  * Wine VST host side.
  */
-int __attribute__((visibility("default"))) main(int argc, char* argv[]) {
+int __attribute__((visibility("default")))
+#ifdef WINE_USE_CDECL
+__cdecl
+#endif
+    main(int argc, char* argv[]) {
     set_realtime_priority();
 
     // Instead of directly hosting a plugin, this process will receive a UNIX

src/wine-host/individual-host.cpp

@@ -29,7 +29,11 @@
  * plugin, and then connect back to the `libyabridge.so` instance that spawned
  * this over the socket.
  */
-int __attribute__((visibility("default"))) main(int argc, char* argv[]) {
+int __attribute__((visibility("default")))
+#ifdef WINE_USE_CDECL
+__cdecl
+#endif
+    main(int argc, char* argv[]) {
     set_realtime_priority();
 
     // We pass the name of the VST plugin .dll file to load and the base