Toolchain: Handle repeated invocations of CMake with -DCMAKE_C_COMPILER

Repeated invocations of `cmake ... -DCMAKE_C_COMPILER=gcc` should not
trigger a "You have changed variables" message even though the cache
value of CMAKE_C_COMPILER changes from '/path/to/gcc' to 'gcc'.

Make repeated invocations of `cmake ... -DCMAKE_C_COMPILER=gcc;-pipe`
not trigger the warning by comparing the compiler name portion of the list to
the compiler being used.

Source/cmGlobalGenerator.cxx

@@ -235,6 +235,14 @@ void cmGlobalGenerator::ResolveLanguageCompiler(const std::string& lang,
   }
   cmProp cname =
     this->GetCMakeInstance()->GetState()->GetInitializedCacheValue(langComp);
+
+  // Split compiler from arguments
+  std::vector<std::string> cnameArgVec;
+  if (cname && !cname->empty()) {
+    cmExpandList(*cname, cnameArgVec);
+    cname = &cnameArgVec.front();
+  }
+
   std::string changeVars;
   if (cname && !optional) {
     std::string cnameString;

Source/cmRulePlaceholderExpander.cxx

@@ -261,7 +261,7 @@ std::string cmRulePlaceholderExpander::ExpandRuleVariable(
       this->VariableMappings["CMAKE_" + compIt->second +
                              "_COMPILE_OPTIONS_SYSROOT"];
 
-    // if there is a required first argument to the compiler add it
+    // if there are required arguments to the compiler add it
     // to the compiler string
     if (!compilerArg1.empty()) {
       ret += " ";