hurd: add gscope support

hurd: add gscope support

* elf/dl-support.c [!THREAD_GSCOPE_IN_TCB] (_dl_thread_gscope_count):
Define variable.
* sysdeps/generic/ldsodefs.h [!THREAD_GSCOPE_IN_TCB] (struct
rtld_global): Add _dl_thread_gscope_count member.
* sysdeps/mach/hurd/tls.h: Include <atomic.h>.
[!defined __ASSEMBLER__] (THREAD_GSCOPE_GLOBAL, THREAD_GSCOPE_SET_FLAG,
THREAD_GSCOPE_RESET_FLAG, THREAD_GSCOPE_WAIT): Define macros.
* sysdeps/generic/tls.h: Document THREAD_GSCOPE_IN_TCB.
* sysdeps/aarch64/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/alpha/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/arm/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/hppa/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/i386/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/ia64/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/m68k/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/microblaze/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/mips/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/nios2/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/powerpc/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/riscv/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/s390/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/sh/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/sparc/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/tile/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.
* sysdeps/x86_64/nptl/tls.h: Define THREAD_GSCOPE_IN_TCB to 1.