www/mod_http2: fix build on armv6/armv7

• also incidentally fix the build on powerpc

Approved by: portmgr (build fix blanket)
MFH: 2023Q4

(cherry picked from commit be0250d4a2c6ead8aabaf49c046aa401e696d610)
(cherry picked from commit 6f2112f80c3937bcf1d42bd7a18a742b36b3a27b)