lib/libc: implement C23 memalignment()

This new function computes the alignment of a pointer.
It is part of ISO/IEC 9899:2024, the new C standard.
If the pointer is a null pointer, null is returned.
I have tried to write an implementation that can cope
with traditional address-based architectures, even if
size_t and uintptr_t are of different length.  Adjustments
may be needed for CHERI though.

A man page is provided, too.  No unit test for now.

Reviewed by:	kib, imp, ziaee (manpages), pauamma@gundo.com
Approved by:	markj (mentor)
MFC after:	1 month
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D53673

(cherry picked from commit 6c57e368eb1777f6097158eeca2fcc175d068dba)

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/libc/stdlib/Symbol.map b/lib/libc/stdlib/Symbol.map
index 53d71bcafb7d..8b7e97c3cbdc 100644
--- a/lib/libc/stdlib/Symbol.map
+++ b/lib/libc/stdlib/Symbol.map
@@ -132,6 +132,7 @@ FBSD_1.8 {
 };
 
 FBSD_1.9 {
+	memalignment;
 	recallocarray;
 };