Fix nativeaot libraries test cross-build (#84870)

Author: sbomer

eng/testing/tests.singlefile.targets

@@ -23,7 +23,7 @@
 
   <PropertyGroup Condition="'$(TestNativeAot)' == 'true'">
     <IlcToolsPath>$(CoreCLRILCompilerDir)</IlcToolsPath>
-    <IlcToolsPath Condition="'$(TargetArchitecture)' != '$(BuildArchitecture)'">$(CoreCLRCrossILCompilerDir)</IlcToolsPath>
+    <IlcToolsPath Condition="'$(CrossBuild)' == 'true' or '$(TargetArchitecture)' != '$(BuildArchitecture)'">$(CoreCLRCrossILCompilerDir)</IlcToolsPath>
     <SysRoot Condition="('$(CrossBuild)' == 'true' or '$(BuildArchitecture)' != '$(TargetArchitecture)') and '$(HostOS)' != 'windows'">$(ROOTFS_DIR)</SysRoot>
     <IlcBuildTasksPath>$(CoreCLRILCompilerDir)netstandard/ILCompiler.Build.Tasks.dll</IlcBuildTasksPath>
     <IlcSdkPath>$(CoreCLRAotSdkDir)</IlcSdkPath>
@@ -36,6 +36,34 @@
     <SuppressAotAnalysisWarnings>true</SuppressAotAnalysisWarnings>
   </PropertyGroup>
 
+  <!-- Needed for the amd64 -> amd64 musl cross-build to pass the target flag. -->
+  <Target Name="_FixIlcTargetTriple"
+          AfterTargets="SetupOSSpecificProps"
+          Condition="'$(CrossBuild)' == 'true' and '$(HostOS)' != 'windows'">
+    <!-- Compute CrossCompileRid, and copy the downstream logic as-is. -->
+    <PropertyGroup>
+      <CrossCompileRid>$(RuntimeIdentifier)</CrossCompileRid>
+
+      <CrossCompileArch />
+      <CrossCompileArch Condition="$(CrossCompileRid.EndsWith('-x64'))">x86_64</CrossCompileArch>
+      <CrossCompileArch Condition="$(CrossCompileRid.EndsWith('-arm64')) and '$(_IsApplePlatform)' != 'true'">aarch64</CrossCompileArch>
+      <CrossCompileArch Condition="$(CrossCompileRid.EndsWith('-arm64')) and '$(_IsApplePlatform)' == 'true'">arm64</CrossCompileArch>
+
+      <TargetTriple />
+      <TargetTriple Condition="'$(CrossCompileArch)' != ''">$(CrossCompileArch)-linux-gnu</TargetTriple>
+      <TargetTriple Condition="'$(CrossCompileArch)' != '' and ($(CrossCompileRid.StartsWith('linux-musl')) or $(CrossCompileRid.StartsWith('alpine')))">$(CrossCompileArch)-alpine-linux-musl</TargetTriple>
+      <TargetTriple Condition="'$(CrossCompileArch)' != '' and ($(CrossCompileRid.StartsWith('freebsd')))">$(CrossCompileArch)-unknown-freebsd12</TargetTriple>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <LinkerArg Include="--target=$(TargetTriple)" Condition="'$(TargetOS)' != 'osx' and '$(TargetTriple)' != ''" />
+    </ItemGroup>
+  </Target>
+
+  <ItemGroup Condition="'$(NativeAotSupported)' == 'true'">
+    <CustomLinkerArg Condition="'$(CrossBuild)' == 'true' and '$(_hostArchitecture)' == '$(_targetArchitecture)' and '$(_hostOS)' != 'windows'" Include="--gcc-toolchain=$(ROOTFS_DIR)/usr" />
+  </ItemGroup>
+
   <PropertyGroup Condition="'$(PublishSingleFile)' == 'true' or '$(TestNativeAot)' == 'true'">
     <DefineConstants>$(DefineConstants);SINGLE_FILE_TEST_RUNNER</DefineConstants>
   </PropertyGroup>