doc/gccgo: change gold build instructions to use Git repository

Use the binutils Git repository instead of CVS.

Change-Id: I10100ca44d64ab3621367d1d4ac9e9a50d212d0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/237839
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: tklauser

doc/gccgo_install.html

@@ -137,13 +137,10 @@ <h3 id="Gold">Gold</h3>
 </p>
 
 <pre>
-cvs -z 9 -d :pserver:[email protected]:/cvs/src login
-[password is "anoncvs"]
-[The next command will create a directory named src, not binutils]
-cvs -z 9 -d :pserver:[email protected]:/cvs/src co binutils
+git clone git://sourceware.org/git/binutils-gdb.git
 mkdir binutils-objdir
 cd binutils-objdir
-../src/configure --enable-gold=default --prefix=/opt/gold
+../binutils-gdb/configure --enable-gold=default --prefix=/opt/gold
 make
 make install
 </pre>