Log Message:
Fix build failure on NetBSD/arm 6.1.  PR/47941
 - fix configure scripts to detect !G_ATOMIC_LOCK_FREE correctly
   (use AC_TRY_LINK rather than AC_TRY_COMPILE to see if symbols are defined)
 - fix prototype mismatches in !G_ATOMIC_LOCK_FREE case
   (note no binary changes in G_ATOMIC_LOCK_FREE case)

"please commit it" from agc@.