Addressing a first batch of feedback.

include/grpc/support/atm.h

include/grpc/support/sync.h

include/grpc/support/sync_posix.h

include/grpc/support/sync_win32.h

include/grpc/support/time.h

src/core/support/log_win32.c

src/core/support/string_posix.c

src/core/support/sync.c

src/core/support/time.c

src/cpp/server/thread_pool.cc

test/core/support/time_test.c