build: fix corrupted patch causing bootstrap failures

The patch was corrupted in commit v8.21-50-g7b65f8e

* gl/modules/tempname.diff: Fix the offsets so that the patch
applies cleanly.  Note that this was only apparent with patch < 2.6.
With patch >= 2.6, patch will not indicate an error applying
the second hunk of the patch and silently ignore it.
I double checked that all patches now apply cleanly by adjusting
gnulib-tool to run patch with --fuzz=0 which might be advisable
going forward, even on a per project basis.
The silent ignoring of hunks by newer patch(1) has been reported.
Fixes http://bugs.gnu.org/15255

gl/modules/tempname.diff

@@ -2,7 +2,7 @@ diff --git a/modules/tempname b/modules/tempname
 index 7fafd72..4703517 100644
 --- a/modules/tempname
 +++ b/modules/tempname
-@@ -1,2 +1,2 @@
+@@ -1,5 +1,5 @@
  Description:
 -gen_tempname() function: create a private temporary file or directory.
 +gen_tempname, gen_tempname_len: create a private temporary file or directory.