VS: Fix mapping of -Qspectre- flag

The mapping for this flag was added by commit 43aa632 (VS: Populate
`-Qspectre-` flag table entry for v142, 2019-01-24, v3.14.0-rc1~74^2~7).
However, it did not do anything because the special logic added by
commit bb60ed6 (VS: Add flag table entry for -Qspectre, 2018-10-08,
v3.13.0-rc1~4^2) to move the `SpectreMitigation` element from
`ClCompile` to the top level only handled the presence of the setting
and not its value.  Extend the special logic to carry the value too.

Fixes: #19535

Author: bradking

Source/cmVisualStudio10TargetGenerator.cxx

@@ -1229,8 +1229,11 @@ void cmVisualStudio10TargetGenerator::WriteMSToolConfigurationValues(
   if (this->IPOEnabledConfigurations.count(config) > 0) {
     e1.Element("WholeProgramOptimization", "true");
   }
-  if (this->SpectreMitigationConfigurations.count(config) > 0) {
-    e1.Element("SpectreMitigation", "Spectre");
+  {
+    auto s = this->SpectreMitigation.find(config);
+    if (s != this->SpectreMitigation.end()) {
+      e1.Element("SpectreMitigation", s->second);
+    }
   }
 }
 
@@ -2760,8 +2763,8 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
     }
   }
 
-  if (clOptions.HasFlag("SpectreMitigation")) {
-    this->SpectreMitigationConfigurations.insert(configName);
+  if (const char* s = clOptions.GetFlag("SpectreMitigation")) {
+    this->SpectreMitigation[configName] = s;
     clOptions.RemoveFlag("SpectreMitigation");
   }
 

Source/cmVisualStudio10TargetGenerator.h

@@ -215,7 +215,7 @@ class cmVisualStudio10TargetGenerator
   unsigned int NsightTegraVersion[4];
   bool TargetCompileAsWinRT;
   std::set<std::string> IPOEnabledConfigurations;
-  std::set<std::string> SpectreMitigationConfigurations;
+  std::map<std::string, std::string> SpectreMitigation;
   cmGlobalVisualStudio10Generator* const GlobalGenerator;
   cmLocalVisualStudio10Generator* const LocalGenerator;
   std::set<std::string> CSharpCustomCommandNames;

Tests/RunCMake/VS10Project/RunCMakeTest.cmake

@@ -26,3 +26,7 @@ run_cmake(VsPackageReferences)
 if(CMAKE_C_COMPILER_ID STREQUAL "MSVC" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.05)
   run_cmake(VsJustMyCode)
 endif()
+
+if(CMAKE_C_COMPILER_ID STREQUAL "MSVC" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.20)
+  run_cmake(VsSpectreMitigation)
+endif()

Tests/RunCMake/VS10Project/VsSpectreMitigation-check.cmake

@@ -0,0 +1,30 @@
+macro(VsSpectreMitigation_check tgt spectre_expect)
+  set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/${tgt}.vcxproj")
+  if(NOT EXISTS "${vcProjectFile}")
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not exist.")
+    return()
+  endif()
+
+  set(HAVE_SpectreMitigation 0)
+
+  file(STRINGS "${vcProjectFile}" lines)
+  foreach(line IN LISTS lines)
+    if(line MATCHES "^ *<SpectreMitigation>([^<>]+)</SpectreMitigation>")
+      set(spectre_actual "${CMAKE_MATCH_1}")
+      if(NOT "${spectre_actual}" STREQUAL "${spectre_expect}")
+        set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj has <SpectreMitigation> '${spectre_actual}', not '${spectre_expect}'.")
+        return()
+      endif()
+      set(HAVE_SpectreMitigation 1)
+      break()
+    endif()
+  endforeach()
+
+  if(NOT HAVE_SpectreMitigation AND NOT "${spectre_expect}" STREQUAL "")
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not have a <SpectreMitigation> field.")
+    return()
+  endif()
+endmacro()
+
+VsSpectreMitigation_check(SpectreMitigationOn-C "Spectre")
+VsSpectreMitigation_check(SpectreMitigationOff-C "false")

Tests/RunCMake/VS10Project/VsSpectreMitigation.cmake

@@ -0,0 +1,8 @@
+set(CMAKE_CONFIGURATION_TYPES Debug)
+enable_language(C)
+
+add_library(SpectreMitigationOn-C empty.c)
+target_compile_options(SpectreMitigationOn-C PRIVATE -Qspectre)
+
+add_library(SpectreMitigationOff-C empty.c)
+target_compile_options(SpectreMitigationOff-C PRIVATE -Qspectre-)