doc: mention -compressdwarf=false on gdb page

Update #11799

Change-Id: I2646a52bfb8aecb67a664a7c6fba25511a1aa49f
Reviewed-on: https://go-review.googlesource.com/138182
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: David Chase <drchase@google.com>

Author: ianlancetaylor

doc/debugging_with_gdb.html

@@ -180,6 +180,15 @@ <h3 id="Known_Issues">Known Issues</h3>
 that needs to be quoted.  It objects even more strongly to method names of
 the form <code>pkg.(*MyType).Meth</code>.
 <li>All global variables are lumped into package <code>"main"</code>.</li>
+<li>As of Go 1.11, debug information is compressed by default.
+Older versions of gdb, such as the one available by default on MacOS,
+do not understand the compression.
+You can generate uncompressed debug information by using <code>go
+build -ldflags=-compressdwarf=false</code>.
+(For convenience you can put the <code>-ldflags</code> option in
+the <a href="/cmd/go/#hdr-Environment_variables"><code>GOFLAGS</code>
+environment variable</a> so that you don't have to specify it each time.)
+</li>
 </ol>
 
 <h2 id="Tutorial">Tutorial</h2>