Revert 215743 "Don't pass /safeseh to the linker when using clan..."

This is no longer needed.  Clang is SEH safe because it doesn't support
SEH and therefore has no SEH handlers to register in .sxdata.  It emits
the @feat.00 symbol to let the linker know that it is SEH safe.

> Don't pass /safeseh to the linker when using clang on Windows
> 
> It does not generate SEH safe code at the moment.
> 
> R=scottmg@chromium.org
> BUG=82385
> 
> Review URL: https://codereview.chromium.org/21910008

TBR=scottmg@chromium.org

Review URL: https://codereview.chromium.org/26864005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228004 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228004