Fixed errors in documentation that caused configure script to fail when bootstrapping for ARM build

texinfo 5 has changed syntax for certain commands which led to failure when
building binutils because the documentation could not be built.
Upstream report: https://sourceware.org/bugzilla/show_bug.cgi?id=15212.

Signed-off-by: Adrien Destugues <pulkomandy@pulkomandy.tk>