Building GCC 4.9 RC with in-tree binutils

[Matt Godbolt]

Hi all,

I'm trying to build the RC of 4.9 with the latest released binutils
(2.24) linked in-tree (using the symlink-all-the-binutils-files-into
the root of gcc build trick).

However, during the second stage, binutils fails to compile due to
errors of the form:
../bfd/bfd.h:304:75: error: right-hand operand of comma expression has
no effect [-Werror=unused-value]
   #define bfd_set_section_userdata(bfd, ptr, val) (((ptr)->userdata =
(val)),TRUE)

I've seen various posts on the net about this issue but no obvious
workable solution.  I've tried setting CFLAGS, CXXFLAGS and the
equivalent *_FOR_TARGET to include '-Wno-error' but to no avail.

Can someone give me a gentle nudge in the right direction here please?

Thanks in advance,

Matt