cmMakefile: Return a string from GetDefineFlags

Flip condition in GHS for readability.

Source/cmGhsMultiTargetGenerator.cxx

@@ -244,7 +244,7 @@ void cmGhsMultiTargetGenerator::SetCompilerFlags(std::string const& config,
       flags, this->GeneratorTarget, lang);
 
     // Append old-style preprocessor definition flags.
-    if (std::string(" ") != std::string(this->Makefile->GetDefineFlags())) {
+    if (this->Makefile->GetDefineFlags() != " ") {
       this->LocalGenerator->AppendFlags(flags,
                                         this->Makefile->GetDefineFlags());
     }

Source/cmMakefile.h

@@ -447,7 +447,7 @@ public:
   /**
    * Get a list of preprocessor define flags.
    */
-  const char* GetDefineFlags() const { return this->DefineFlags.c_str(); }
+  std::string GetDefineFlags() const { return this->DefineFlags; }
 
   /**
    * Make sure CMake can write this file