None of that worked, use #ifdef __GNUC__ on the manifest.

This means ciolib utilities built with MSVC won't have the right
manifest information, but the documentation is terrible and I can't
figure it out.

src/conio/ciolib.rc

 #include "windows.h"
 
 /* Manifest */
+#ifdef __GNUC__
 1 RT_MANIFEST "ciolib.manifest"
+#endif
 
 /* ========================================================================= */
 /* Icons.                                                                    */

src/conio/conio.props

@@ -9,9 +9,6 @@
     <ClCompile>
       <AdditionalIncludeDirectories>$(MSBuildThisFileDirectory);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
     </ClCompile>
-    <Link>
-      <NoWin32Manifest>True</NoWin32Manifest>
-    </Link>
   </ItemDefinitionGroup>
   <ItemGroup />
 </Project>

src/conio/conio_gdi.props

@@ -9,15 +9,10 @@
     <ClCompile>
       <PreprocessorDefinitions>WITH_GDI;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(MSBuildThisFileDirectory);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-      <NoWin32Manifest>True</NoWin32Manifest>
     </ClCompile>
-    <ResourceCompile>
-      <NoWin32Manifest>True</NoWin32Manifest>
-    </ResourceCompile>
     <Link>
       <AdditionalDependencies>winmm.lib;%(AdditionalDependencies)</AdditionalDependencies>
       <SubSystem>Windows</SubSystem>
-      <NoWin32Manifest>True</NoWin32Manifest>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup />

src/conio/conio_sdl.props

@@ -12,7 +12,6 @@
     </ClCompile>
     <Link>
       <AdditionalDependencies>winmm.lib;%(AdditionalDependencies)</AdditionalDependencies>
-      <NoWin32Manifest>True</NoWin32Manifest>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup />