Add the wide-used alloca() function. As it is highly machine and
compiler dependent, just defer to the compiler builtin. This has
been available since GCC 4 and clang 3.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260409-nolibc-alloca-v1-1-ed02f68dfaf9@weissschuh.net
