Rename go_gccgo_setup to gccgo_install.

R=rsc
CC=go-dev
http://go/go-review/1026009

doc/gccgo_contribute.html

@@ -7,7 +7,7 @@ These are some notes on contributing to the <code>gccgo</code>
 frontend for GCC.  For information on contributing to parts of Go other
 than <code>gccgo</code>, see <a href="contribute.html">Contributing to
 the Go project</a>.  For information on building <code>gccgo</code>
-for yourself, see <a href="go_gccgo_setup.html">Setting up and using
+for yourself, see <a href="gccgo_install.html">Setting up and using
 gccgo</a>.
 </p>
 

doc/install.html

@@ -8,7 +8,7 @@ This document explains how to check out, build, and use the <code>gc</code> Go
 compiler and tools (<code>6g</code>, <code>8g</code> etc.).
 For information on how to use <code>gccgo</code>, a more traditional
 compiler using the GCC back end, see
-<a href="go_gccgo_setup.html">Setting up and using gccgo</a>.
+<a href="gccgo_install.html">Setting up and using gccgo</a>.
 </p>
 
 <h2>Environment variables</h2>
@@ -120,7 +120,7 @@ support for segmented stacks, and a strong goroutine implementation.
 </p>
 
 <p>
-See the separate <a href="go_gccgo_setup.html"><code>gccgo</code> document</a>
+See the separate <a href="gccgo_install.html"><code>gccgo</code> document</a>
 for details about that compiler and environment.
 </p>