[klibc] malloc: Set errno on failure

malloc() is specified to set errno = ENOMEM on failure, so do that.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

usr/klibc/malloc.c

@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include <sys/mman.h>
 #include <assert.h>
+#include <errno.h>
 #include "malloc.h"
 
 /* Both the arena list and the free memory list are double linked
@@ -169,6 +170,7 @@ void *malloc(size_t size)
 #endif
 
 	if (fp == (struct free_arena_header *)MAP_FAILED) {
+		errno = ENOMEM;
 		return NULL;	/* Failed to get a block */
 	}