[m-rev.] for review: Do not define _DYNAMIC when linking statically on Linux.

[Julien Fischer]

On Fri, 12 Jan 2018, Peter Wang wrote:

> We used to manually define the symbol _DYNAMIC (to zero) when
> statically linking on Linx to avoid undefined references to _DYNAMIC
> from boehm_gc/dyn_load.c. That has been unnecessary since gc5.0alpha3
> when dyn_load.c declared _DYNAMIC as a weak symbol.
>
> When a program is statically linked to musl, _DYNAMIC is defined with a
> non-zero address. Forcing its address to zero caused the program to
> crash during GC initialisation. Fixed now.
>
> configure.ac:
>    As above.

That's fine.

Julien.