Fix -flto and RTS coverage detection

Suppress a spurious clang warning

lib/rts.c

@@ -78,7 +78,7 @@
 extern "C" {
 #endif
 
-extern void sail_rts_set_coverage_file(char *output_file);
+extern void (*sail_rts_set_coverage_file)(const char *);
 
 static uint64_t g_elf_entry;
 uint64_t g_cycle_count = 0;
@@ -725,11 +725,14 @@ int process_arguments(int argc, char *argv[])
       break;
 
     case 'c':
-      if (&sail_rts_set_coverage_file) {
+      #pragma clang diagnostic push
+      #pragma clang diagnostic ignored "-Wtautological-pointer-compare"
+      if (&sail_rts_set_coverage_file != NULL) {
         sail_rts_set_coverage_file(optarg);
       } else {
         fprintf(stderr, "Ignoring flag -c %s. Requires the model to be compiled with coverage\n", optarg);
       }
+      #pragma clang diagnostic pop
       break;
 
     case 'v':

src/sail_c_backend/c_backend.ml

@@ -2009,10 +2009,8 @@ let compile_ast env effect_info output_chan c_includes ast =
       let header = string "#include \"sail_coverage.h\"" in
       (* Generate a hook for the RTS to call if we have coverage
          enabled, so it can set the output file with an option. *)
-      let coverage_hook =
-        string "void sail_rts_set_coverage_file(char *output_file) { sail_set_coverage_file(output_file); }"
-      in
-      let no_coverage_hook = string "void (*sail_rts_set_coverage_file)(char *) = NULL;" in
+      let coverage_hook = string "void (*sail_rts_set_coverage_file)(const char *) = &sail_set_coverage_file;" in
+      let no_coverage_hook = string "void (*sail_rts_set_coverage_file)(const char *) = NULL;" in
       match !opt_branch_coverage with
       | Some _ -> if !opt_no_rts then [header] else [header; coverage_hook]
       | None -> if !opt_no_rts then [] else [no_coverage_hook]