/usr/include/grpc/support/ is in libgrpc-dev 1.3.2-1.1~build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/grpc/support/alloc.h
/usr/include/grpc/support/atm.h
/usr/include/grpc/support/atm_gcc_atomic.h
/usr/include/grpc/support/atm_gcc_sync.h
/usr/include/grpc/support/atm_windows.h
/usr/include/grpc/support/avl.h
/usr/include/grpc/support/cmdline.h
/usr/include/grpc/support/cpu.h
/usr/include/grpc/support/histogram.h
/usr/include/grpc/support/host_port.h
/usr/include/grpc/support/log.h
/usr/include/grpc/support/log_windows.h
/usr/include/grpc/support/port_platform.h
/usr/include/grpc/support/string_util.h
/usr/include/grpc/support/subprocess.h
/usr/include/grpc/support/sync.h
/usr/include/grpc/support/sync_generic.h
/usr/include/grpc/support/sync_posix.h
/usr/include/grpc/support/sync_windows.h
/usr/include/grpc/support/thd.h
/usr/include/grpc/support/time.h
/usr/include/grpc/support/tls.h
/usr/include/grpc/support/tls_gcc.h
/usr/include/grpc/support/tls_msvc.h
/usr/include/grpc/support/tls_pthread.h
/usr/include/grpc/support/useful.h