perf/unwind: include errno.h unconditionally

EINVAL is used in other branches as well. Without errno.h, it ends up
undefined and the build fails. This happens with 32-bit ROSA kernels, for
example.

diff --git a/tools/perf/arch/x86/util/unwind-libunwind.c b/tools/perf/arch/x86/util/unwind-libunwind.c
index 9c917f80c906..7bff51b9b547 100644
--- a/tools/perf/arch/x86/util/unwind-libunwind.c
+++ b/tools/perf/arch/x86/util/unwind-libunwind.c
@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <errno.h> /* for EINVAL */
+
 #ifndef REMOTE_UNWIND_LIBUNWIND
-#include <errno.h>
 #include <libunwind.h>
 #include "perf_regs.h"
 #include "../../util/unwind.h"