libc: newlib: limits.h: include posix limits from zephyr

Newlib does not seem to define a number of mandatory POSIX limits
(e.g. minimum values).

Include Zephyr's POSIX definitions in an override of Newlib's limits.h
(when the appropriate application conformance macro is provided).

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>

Author: cfriedt

lib/libc/newlib/include/limits.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright The Zephyr Project Contributors
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_LIB_LIBC_NEWLIB_INCLUDE_LIMITS_H_
+#define ZEPHYR_LIB_LIBC_NEWLIB_INCLUDE_LIMITS_H_
+
+#include_next <limits.h>
+#include <zephyr/posix/posix_limits.h>
+
+#endif /* ZEPHYR_LIB_LIBC_NEWLIB_INCLUDE_LIMITS_H_ */