[patch,driver] Make the driver output environment variables when verbose

[François-Xavier Coudert]

This patch allows the driver to output the changes it makes to
environment when invoked with -v. I looked at the doc, but it doesn't
say exactly what -v does anyway, so I don't think we need to document
that particular behaviour.

Bootstrapped and regtested on x86_64-linux, OK to commit?

FX



:ADDPATCH driver:
-------------- next part --------------
A non-text attachment was scrubbed...
Name: putenv.ChangeLog
Type: application/octet-stream
Size: 303 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20070831/3d182541/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: putenv.diff
Type: application/octet-stream
Size: 2531 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20070831/3d182541/attachment-0001.obj>