stdlib: set errno=ENOMEM after failed malloc()

src/libc/stdlib/target/gint/malloc.c

@@ -1,8 +1,12 @@
 #include <stdlib.h>
+#include <errno.h>
 
 extern void *kmalloc(size_t size, char const *arena_name);
 
 void *malloc(size_t size)
 {
-	return kmalloc(size, NULL);
+	void *ptr = kmalloc(size, NULL);
+	if(ptr == NULL)
+		errno = ENOMEM;
+	return ptr;
 }