Implement [ap_]atomics for [u]int/[u]long/size_t and use them for (some) proxy_worker_shared fields #626

Job	Run time
Empty APLOGNO() test	28s
Default	5m 29s
All-static modules	3m 39s
Prefork MPM, all-modules (except cgid)	6m 14s
Worker MPM, all-modules	3m 57s
Shared MPMs, all-modules	4m 8s
Event MPM, all-modules, mod_cgid only	3m 52s
Event MPM, all-modules, no CMSG_DATA	5m 33s
Default, all-modules + install	6m 40s
Default, all-modules, random test order	6m 4s
GCC 10 maintainer-mode w/-Werror, install + VPATH	3m 36s
All-modules, APR 1.7.4, APR-util 1.6.3	5m 36s
APR 1.8.x, APR-util 1.7.x	6m 13s
Pool-debug	5m 52s
Shared MPMs (event), pool-debug, SSL/TLS variants	13m 34s
Shared MPMs (worker), pool-debug, SSL/TLS variants	10m 49s
Shared MPMs (prefork), pool-debug, SSL/TLS variants	13m 21s
litmus WebDAV tests	2m 14s
litmus WebDAV tests, APR trunk, LMDB	3m 1s
Regenerate ap_expr	4m 44s
APR 1.7.4, APR-util 1.6.3, LDAP	7m 25s
APR trunk thread debugging	5m 40s
UBSan	6m 8s
ASan	6m 17s
ASan, pool-debug	7m 59s
HTTP/2 test suite	14m 25s
MOD_TLS test suite	7m 38s
	2h 50m 36s

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