Fix some generator crashes on undefined CMAKE_BUILD_TYPE

Since commit 84fdc9921 (stringapi: Pass configuration names as strings,
2014-02-09), it is not safe to use GetDefinition("CMAKE_BUILD_TYPE")
without checking the return value.  Use GetSafeDefinition instead so
that a missing definition is treated as an empty string like code paths
did prior to the above commit.

Reported-by: Richard Wirth <[email protected]>

Source/cmExtraCodeBlocksGenerator.cxx

@@ -574,7 +574,7 @@ void cmExtraCodeBlocksGenerator::AppendTarget(cmGeneratedFileStream& fout,
         }
       }
 
-    const char* buildType = makefile->GetDefinition("CMAKE_BUILD_TYPE");
+    std::string buildType = makefile->GetSafeDefinition("CMAKE_BUILD_TYPE");
     std::string location;
     if ( target->GetType()==cmTarget::OBJECT_LIBRARY)
       {

Source/cmExtraEclipseCDT4Generator.cxx

@@ -968,7 +968,7 @@ void cmExtraEclipseCDT4Generator::CreateCProjectFile() const
         continue;
         }
       std::vector<std::string> includeDirs;
-      const char *config = mf->GetDefinition("CMAKE_BUILD_TYPE");
+      std::string config = mf->GetSafeDefinition("CMAKE_BUILD_TYPE");
       (*it)->GetIncludeDirectories(includeDirs, l->second, "C", config);
       this->AppendIncludeDirectories(fout, includeDirs, emmited);
       }

Source/cmLocalGenerator.cxx

@@ -1861,7 +1861,7 @@ void cmLocalGenerator::OutputLinkLibraries(std::string& linkLibraries,
                              ((useWatcomQuote) ? WATCOMQUOTE : SHELL);
   bool escapeAllowMakeVars = !forResponseFile;
   cmOStringStream fout;
-  const char* config = this->Makefile->GetDefinition("CMAKE_BUILD_TYPE");
+  std::string config = this->Makefile->GetSafeDefinition("CMAKE_BUILD_TYPE");
   cmComputeLinkInformation* pcli = tgt.Target->GetLinkInformation(config);
   if(!pcli)
     {