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
diff --git a/scripts/Makefile b/scripts/Makefile
index 1b26617..fd0d53d 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -7,6 +7,7 @@
 # conmakehash:   Create chartable
 # conmakehash:	 Create arrays for initializing the kernel console tables
 # docproc:       Used in Documentation/DocBook
+# check-lc_ctype: Used in Documentation/DocBook
 
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include
 
@@ -27,14 +28,16 @@
 always		:= $(hostprogs-y) $(hostprogs-m)
 
 # The following hostprogs-y programs are only build on demand
-hostprogs-y += unifdef docproc
+hostprogs-y += unifdef docproc check-lc_ctype
 
 # These targets are used internally to avoid "is up to date" messages
-PHONY += build_unifdef build_docproc
+PHONY += build_unifdef build_docproc build_check-lc_ctype
 build_unifdef: $(obj)/unifdef
 	@:
 build_docproc: $(obj)/docproc
 	@:
+build_check-lc_ctype: $(obj)/check-lc_ctype
+	@:
 
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-y                     += mod
diff --git a/scripts/check-lc_ctype.c b/scripts/check-lc_ctype.c
new file mode 100644
index 0000000..9097ff5
--- /dev/null
+++ b/scripts/check-lc_ctype.c
@@ -0,0 +1,11 @@
+/*
+ * Check that a specified locale works as LC_CTYPE.  Used by the
+ * DocBook build system to probe for C.UTF-8 support.
+ */
+
+#include <locale.h>
+
+int main(void)
+{
+	return !setlocale(LC_CTYPE, "");
+}