0.3.0: converge relibc to upstream 0.6.0 + Red Bear patches

tests/malloc/usable_size.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <string.h>
+#include <assert.h>
+
+int main(void) {
+    size_t request_size = 27;
+    char *ptr = (char *)malloc(request_size);
+
+    if (!ptr) {
+        fprintf(stderr, "Allocation failed\n");
+        return 1;
+    }
+
+    size_t actual_size = malloc_usable_size(ptr);
+
+    printf("malloc: %zu bytes\n", request_size);
+    printf("malloc_usable_size: %zu bytes\n", actual_size);
+
+    assert(actual_size >= request_size);
+    memset(ptr, 'A', actual_size); 
+    ptr[actual_size - 1] = '\0';
+
+    assert(ptr[0] == 'A');
+    assert(ptr[actual_size - 2] == 'A');
+    assert(ptr[actual_size - 1] == '\0');
+    free(ptr);
+
+    return 0;
+}