BUG/MINOR: compat: make sure __WORDSIZE is always defined

BUG/MINOR: compat: make sure __WORDSIZE is always defined

-Wundef triggered on a MIPS-based musl build on __WORDSIZE that's used
in ultoa_o() and some Lua initialization. The former will fail to convert
integers larger to 1 billion to proper string in this case. Let's make
sure this macro is defined and fall back to values determined from
__SIZEOF_LONG__ otherwise. A cleaner long-term approach would consist
in removing all remaining occurrences of this macro.

This can be backported to all versions.

(cherry picked from commit 4f5485bfad8355b7cf2d62a36897558dfc44bcb6)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 3f41b89598ed8978ee878d35b98a5c0e997c3b05)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>