[gfortran,patch] Complete libgfortran namespace separation and version number

[FX Coudert]

ping

> Attached patch does the following three things:
>  - add an undocumented -fallow-leading-underscore option to gfortran,
> for internal use only, until the ISO_C_BINDING patch is commited, that
> allows symbol names to begin with an underscore (note: it does
> explicitely ICE if one of these variables has implicit type)
>  - use this to prefix all libgfortran symbols names with _gfortran_
> (this was not the case before, especially for specifics), achieving
> complete namespace separation for the library
>  - bump the libgfortran version number to 4.3.0
>
> Bootstrapped & regtested on i686-linux. OK for mainline?