Enable building .dll if both 'CustomNativeMain' and 'NativeLib' are s…

…et (#103504)

* Build a .dll if 'CustomNativeMain' is set

* Switch on 'NativeLib' instead for .exe args

* Actually output a .dll if 'NativeLib' is set

---------

Co-authored-by: Jan Kotas <jkotas@microsoft.com>
Co-authored-by: Michal Strehovský <MichalStrehovsky@users.noreply.github.com>

src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.Windows.targets

@@ -92,12 +92,11 @@ The .NET Foundation licenses this file to you under the MIT license.
       <LinkerArg Condition="$(NativeDebugSymbols) == 'true'" Include="/DEBUG" />
       <!-- The runtime is not compatible with jump stubs inserted by incremental linking. -->
       <LinkerArg Include="/INCREMENTAL:NO" />
-      <LinkerArg Condition="'$(LinkerSubsystem)' != ''" Include="/SUBSYSTEM:$(LinkerSubsystem)" />
-      <LinkerArg Condition="'$(OutputType)' == 'WinExe' or '$(OutputType)' == 'Exe'" Include="/ENTRY:$(EntryPointSymbol) /NOEXP /NOIMPLIB" />
+      <LinkerArg Condition="'$(NativeLib)' == '' and '$(LinkerSubsystem)' != ''" Include="/SUBSYSTEM:$(LinkerSubsystem)" />
+      <LinkerArg Condition="'$(NativeLib)' == ''" Include="/ENTRY:$(EntryPointSymbol) /NOEXP /NOIMPLIB /STACK:$(IlcDefaultStackSize)" />
       <LinkerArg Include="/NATVIS:&quot;$(MSBuildThisFileDirectory)NativeAOT.natvis&quot;" />
       <LinkerArg Condition="'$(ControlFlowGuard)' == 'Guard'" Include="/guard:cf" />
       <LinkerArg Condition="'$(_targetArchitecture)' == 'x86'" Include="/safeseh" />
-      <LinkerArg Condition="'$(OutputType)' == 'WinExe' or '$(OutputType)' == 'Exe'" Include="/STACK:$(IlcDefaultStackSize)" />
       <!-- Do not warn if someone declares UnmanagedCallersOnly with an entrypoint of 'DllGetClassObject' and similar -->
       <LinkerArg Include="/IGNORE:4104" />
       <!-- Opt into CETCOMPAT by default. -->

src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets

@@ -62,7 +62,7 @@ The .NET Foundation licenses this file to you under the MIT license.
 
     <IlcOutputFileExt Condition="$(IlcOutputFileExt) == ''">$(NativeObjectExt)</IlcOutputFileExt>
 
-    <IsNativeExecutable Condition="'$(OutputType)' == 'Exe' or '$(OutputType)' == 'WinExe'">true</IsNativeExecutable>
+    <IsNativeExecutable Condition="('$(OutputType)' == 'Exe' or '$(OutputType)' == 'WinExe') and '$(NativeLib)' == ''">true</IsNativeExecutable>
 
     <NativeBinaryExt Condition="'$(IsNativeExecutable)' == 'true' and '$(_targetOS)' == 'win'">.exe</NativeBinaryExt>
     <NativeBinaryExt Condition="'$(IsNativeExecutable)' == 'true' and '$(_targetOS)' != 'win'"></NativeBinaryExt>