make: fix GCC warnings

*** 187,198 ****
          Boolean         stdout_stderr_same;
          Dependency      suffixes;
          Name            suffixes_name;
          Name            sunpro_dependencies;
          Boolean         target_variants;
!         char            *tmpdir = NOCATGETS("/tmp");
!         char            *temp_file_directory = NOCATGETS(".");
          Name            temp_file_name;
          short           temp_file_number;
          time_t          timing_start;
          wchar_t         *top_level_target;
          Boolean         touch;                          /* `-t' */
--- 187,198 ----
          Boolean         stdout_stderr_same;
          Dependency      suffixes;
          Name            suffixes_name;
          Name            sunpro_dependencies;
          Boolean         target_variants;
!         const char      *tmpdir = NOCATGETS("/tmp");
!         const char      *temp_file_directory = NOCATGETS(".");
          Name            temp_file_name;
          short           temp_file_number;
          time_t          timing_start;
          wchar_t         *top_level_target;
          Boolean         touch;                          /* `-t' */