Enable -Wextra in tests.

tests/stdio/fread.c

@@ -10,9 +10,15 @@ int main(void) {
 
     char buf[33] = { 0 };
     for (int i = 1; i <= 32; ++i) {
-        if (fread(buf, 1, i, fp) < 0) {
-            perror("fread");
-            exit(EXIT_FAILURE);
+        size_t nread = fread(buf, 1, i, fp);
+        if (nread == 0) {
+            if (feof(fp)) {
+                fprintf(stderr, "early EOF\n");
+                return EXIT_FAILURE;
+            } else {
+                perror("fread");
+                return EXIT_FAILURE;
+            }
         }
         buf[i] = 0;
 

tests/stdio/freopen.c

@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <wchar.h>
 
@@ -32,7 +33,7 @@ int main(void) {
         &test_reopen_opens_file,
         &test_reopen_resets_orientation,
     };
-    for(int i=0; i<sizeof(tests)/sizeof(int(*)(void)); i++) {
+    for(size_t i = 0; i < sizeof(tests) / sizeof(int(*)(void)); i++) {
         printf("%d\n", (*tests[i])());
     }
 }