cmake: Teach --build mode to load CMAKE_GENERATOR_TOOLSET

Extend the `cmGlobalGenerator::SetGeneratorToolset` signature to
indicate when it is called from `cmake::build`.

Source/cmGlobalGenerator.cxx

@@ -165,7 +165,7 @@ bool cmGlobalGenerator::SetGeneratorPlatform(std::string const& p,
   return false;
 }
 
-bool cmGlobalGenerator::SetGeneratorToolset(std::string const& ts,
+bool cmGlobalGenerator::SetGeneratorToolset(std::string const& ts, bool,
                                             cmMakefile* mf)
 {
   if (ts.empty()) {
@@ -650,7 +650,7 @@ void cmGlobalGenerator::EnableLanguage(
 
     // Tell the generator about the toolset, if any.
     std::string toolset = mf->GetSafeDefinition("CMAKE_GENERATOR_TOOLSET");
-    if (!this->SetGeneratorToolset(toolset, mf)) {
+    if (!this->SetGeneratorToolset(toolset, false, mf)) {
       cmSystemTools::SetFatalErrorOccured();
       return;
     }

Source/cmGlobalGenerator.h

@@ -128,7 +128,8 @@ public:
 
   /** Set the generator-specific toolset name.  Returns true if toolset
       is supported and false otherwise.  */
-  virtual bool SetGeneratorToolset(std::string const& ts, cmMakefile* mf);
+  virtual bool SetGeneratorToolset(std::string const& ts, bool build,
+                                   cmMakefile* mf);
 
   /**
    * Create LocalGenerators and process the CMakeLists files. This does not

Source/cmGlobalGhsMultiGenerator.cxx

@@ -64,8 +64,11 @@ void cmGlobalGhsMultiGenerator::ComputeTargetObjectDirectory(
 }
 
 bool cmGlobalGhsMultiGenerator::SetGeneratorToolset(std::string const& ts,
-                                                    cmMakefile* mf)
+                                                    bool build, cmMakefile* mf)
 {
+  if (build) {
+    return true;
+  }
   std::string tsp; /* toolset path */
 
   this->GetToolset(mf, tsp, ts);

Source/cmGlobalGhsMultiGenerator.h

@@ -58,7 +58,8 @@ public:
   static bool SupportsPlatform() { return true; }
 
   // Toolset / Platform Support
-  bool SetGeneratorToolset(std::string const& ts, cmMakefile* mf) override;
+  bool SetGeneratorToolset(std::string const& ts, bool build,
+                           cmMakefile* mf) override;
   bool SetGeneratorPlatform(std::string const& p, cmMakefile* mf) override;
 
   /**

Source/cmGlobalVisualStudio10Generator.cxx

@@ -193,7 +193,7 @@ static void cmCudaToolVersion(std::string& s)
 }
 
 bool cmGlobalVisualStudio10Generator::SetGeneratorToolset(
-  std::string const& ts, cmMakefile* mf)
+  std::string const& ts, bool build, cmMakefile* mf)
 {
   if (this->SystemIsWindowsCE && ts.empty() &&
       this->DefaultPlatformToolset.empty()) {
@@ -208,6 +208,10 @@ bool cmGlobalVisualStudio10Generator::SetGeneratorToolset(
     return false;
   }
 
+  if (build) {
+    return true;
+  }
+
   if (!this->FindVCTargetsPath(mf)) {
     return false;
   }

Source/cmGlobalVisualStudio10Generator.h

@@ -20,7 +20,8 @@ public:
 
   bool SetSystemName(std::string const& s, cmMakefile* mf) override;
   bool SetGeneratorPlatform(std::string const& p, cmMakefile* mf) override;
-  bool SetGeneratorToolset(std::string const& ts, cmMakefile* mf) override;
+  bool SetGeneratorToolset(std::string const& ts, bool build,
+                           cmMakefile* mf) override;
 
   std::vector<GeneratedMakeCommand> GenerateBuildCommand(
     const std::string& makeProgram, const std::string& projectName,

Source/cmGlobalXCodeGenerator.cxx

@@ -267,7 +267,7 @@ std::string cmGlobalXCodeGenerator::FindXcodeBuildCommand()
 }
 
 bool cmGlobalXCodeGenerator::SetGeneratorToolset(std::string const& ts,
-                                                 cmMakefile* mf)
+                                                 bool build, cmMakefile* mf)
 {
   if (ts.find_first_of(",=") != std::string::npos) {
     std::ostringstream e;
@@ -283,6 +283,9 @@ bool cmGlobalXCodeGenerator::SetGeneratorToolset(std::string const& ts,
     return false;
   }
   this->GeneratorToolset = ts;
+  if (build) {
+    return true;
+  }
   if (!this->GeneratorToolset.empty()) {
     mf->AddDefinition("CMAKE_XCODE_PLATFORM_TOOLSET", this->GeneratorToolset);
   }

Source/cmGlobalXCodeGenerator.h

@@ -103,7 +103,8 @@ public:
 
   bool ShouldStripResourcePath(cmMakefile*) const override;
 
-  bool SetGeneratorToolset(std::string const& ts, cmMakefile* mf) override;
+  bool SetGeneratorToolset(std::string const& ts, bool build,
+                           cmMakefile* mf) override;
   void AppendFlag(std::string& flags, std::string const& flag) const;
 
 protected:

Source/cmake.cxx

@@ -2620,6 +2620,14 @@ int cmake::Build(int jobs, const std::string& dir,
       return 1;
     }
   }
+  const char* cachedGeneratorToolset =
+    this->State->GetCacheEntryValue("CMAKE_GENERATOR_TOOLSET");
+  if (cachedGeneratorToolset) {
+    cmMakefile mf(gen, this->GetCurrentSnapshot());
+    if (!gen->SetGeneratorToolset(cachedGeneratorToolset, true, &mf)) {
+      return 1;
+    }
+  }
   std::string output;
   std::string projName;
   const char* cachedProjectName =