[PATCH v4] Enable VDSO on x86_64 statically linked programs.

[Florian Weimer]

* Rafael Avila de Espindola:

> diff --git a/Makeconfig b/Makeconfig
> index fbcf69e7c2..61712dc35e 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -999,7 +999,7 @@ ifeq (yes,$(build-shared))
>  # Under --enable-shared, we will build a shared library of PIC objects.
>  # The PIC object files are named foo.os.
>  object-suffixes += .os
> -CPPFLAGS-.os = -DPIC -DSHARED
> +CPPFLAGS-.os = -DPIC -DSHARED -DUSE_VSYSCALL
>  CFLAGS-.os = $(filter %frame-pointer,$(+cflags)) $(pic-ccflag)
>  libtype.os := lib%_pic.a
>  # This can be changed by a sysdep makefile

This doesn't seem to be the right place to define the macro.  We also
prefer macros that are always defined and which change there value
between 0 and 1.

USE_VSYSCALL seems to be a Linux thing and thus should go into
sysdeps/unix/sysv/linux.

It may be clearer to define

#define USE_VSYSCALL (defined (SHARED) || ALWAYS_USE_VSYSCALL)

and then default ALWAYS_USE_VSYSCALL to 0 and override that to 1 for
x86_64.

Thanks,
Florian