try_compile: add missing fclose() to recently added error case

In commit 236133e7 (Handle targets in the LINK_LIBRARIES of try_compile,
2013-02-09) an error return case was added without closing the file in
progress.  Add the missing fclose() call.

Spotted by sevenhill.

Source/cmCoreTryCompile.cxx

@@ -326,6 +326,7 @@ int cmCoreTryCompile::TryCompileCode(std::vector<std::string> const& argv)
         {
         this->Makefile->IssueMessage(cmake::FATAL_ERROR,
                                      "could not write export file.");
+        fclose(fout);
         return -1;
         }
       fprintf(fout,