VS: Don't set LinkToolExe for targets that don't drive linking

A pure ASM_NASM target has no linker of its own, so emitting
CMAKE_LINKER as <LinkToolExe> broke the build (TRK0005) when it was
not found.  Let MSBuild link via the toolset, as MSVC C/CXX targets
already do.

Fixes: #27458

Source/cmGeneratorTarget.cxx

@@ -4094,6 +4094,12 @@ std::string cmGeneratorTarget::GetLinkerTool(std::string const& lang,
     "CMAKE_", lang, this->IsDeviceLink() ? "_DEVICE_" : "_", "LINK_MODE");
   auto mode = this->Makefile->GetDefinition(linkMode);
   if (!mode || mode != "LINKER"_s) {
+    // On the Visual Studio generators the project links via the platform
+    // toolset, so languages without a LINKER-mode toolchain (e.g. ASM_NASM)
+    // must not force a linker; defer to the toolset's default.
+    if (this->GetGlobalGenerator()->IsVisualStudio()) {
+      return std::string{};
+    }
     return this->Makefile->GetDefinition("CMAKE_LINKER");
   }
 

Tests/RunCMake/VS10Project/RunCMakeTest.cmake

@@ -18,6 +18,7 @@ run_cmake(VsCSharpCompilerOpts)
 run_cmake(ExplicitCMakeLists)
 run_cmake(InterfaceLibSources)
 run_cmake(NoImpLib)
+run_cmake(VsNASMLinkTool)
 run_cmake(RuntimeLibrary)
 run_cmake(SourceGroupCMakeLists)
 run_cmake(SourceGroupTreeCMakeLists)

Tests/RunCMake/VS10Project/VsNASMLinkTool-check.cmake

@@ -0,0 +1,13 @@
+set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/nasmexe.vcxproj")
+if(NOT EXISTS "${vcProjectFile}")
+  # No ASM_NASM compiler was available, so there is nothing to verify.
+  return()
+endif()
+
+file(STRINGS "${vcProjectFile}" linkToolExeLines REGEX "<LinkToolExe>")
+if(linkToolExeLines)
+  string(REPLACE ";" "\n  " linkToolExeLines "${linkToolExeLines}")
+  set(RunCMake_TEST_FAILED
+    "nasmexe.vcxproj should not set <LinkToolExe> for an ASM_NASM target; "
+    "MSBuild should link via the toolset.  Found:\n  ${linkToolExeLines}")
+endif()

Tests/RunCMake/VS10Project/VsNASMLinkTool.cmake

@@ -0,0 +1,9 @@
+enable_language(C)
+include(CheckLanguage)
+check_language(ASM_NASM)
+if(CMAKE_ASM_NASM_COMPILER)
+  enable_language(ASM_NASM)
+  # A target whose link language is ASM_NASM must not force CMAKE_LINKER into
+  # <LinkToolExe>; the Visual Studio toolset performs the link.
+  add_executable(nasmexe nasm_main.asm)
+endif()

Tests/RunCMake/VS10Project/nasm_main.asm

@@ -0,0 +1 @@
+section .text