Replace getopt() with our re-entrant variant in the backend

Invent a variant of getopt(3) that is thread-safe

Fix latent bug in get_stats_option_name()

Fix memory leaks from incorrect strsep() uses

Fix strsep() use for SCRAM secrets parsing

Replace remaining strtok() with strtok_r()

Windows replacement for strtok_r()

Replace some strtok() with strsep()

Add PG_TEST_PG_COMBINEBACKUP_MODE to CI tasks

Add PG_TEST_PG_COMBINEBACKUP_MODE

Add pg_combinebackup --copy option

Add headers needed by pg_combinebackup --clone

thread-safety: gmtime_r(), localtime_r()

jsonapi: Use const char *

jsonapi: Use size_t

parse_manifest: Use const char *

Apply COPT to CXXFLAGS as well