DocBook: Use a fixed encoding for output

Currently the encoding of documents generated by DocBook depends on
the current locale.  Make the output reproducible independently of
the locale, by setting the encoding to UTF-8 (LC_CTYPE=C.UTF-8) by
preference, or ASCII (LC_CTYPE=C) as a fallback.

LC_CTYPE can normally be overridden by LC_ALL, but the top-level
Makefile unsets that.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[jc: added check-lc_ctype to .gitignore]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/scripts/.gitignore b/scripts/.gitignore
index 12efbbe..1f78169 100644
--- a/scripts/.gitignore
+++ b/scripts/.gitignore
@@ -8,6 +8,7 @@
 ihex2fw
 recordmcount
 docproc
+check-lc_ctype
 sortextable
 asn1_compiler
 extract-cert