gnu: texinfo: Fix @headings regression.

* gnu/packages/patches/texinfo-headings-single.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/texinfo.scm (texinfo)[source](patches): New field.
* gnu/packages/commencement.scm (texinfo-boot0)[source]: Use BOOTSTRAP-ORIGIN.

gnu/local.mk

@@ -1837,6 +1837,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/tcsh-fix-autotest.patch			\
   %D%/packages/patches/teensy-loader-cli-help.patch		\
   %D%/packages/patches/tensorflow-c-api-fix.patch		\
+  %D%/packages/patches/texinfo-headings-single.patch		\
   %D%/packages/patches/texinfo-5-perl-compat.patch		\
   %D%/packages/patches/telegram-purple-adjust-test.patch	\
   %D%/packages/patches/texi2html-document-encoding.patch	\

gnu/packages/commencement.scm

@@ -2609,6 +2609,7 @@ (define texinfo-boot0
   ;; Also, use (%BOOT0-INPUTS) to avoid building Perl once more.
   (package
     (inherit texinfo)
+    (source (bootstrap-origin (package-source texinfo)))
     (native-inputs '())
     (inputs `(,@(%boot0-inputs)
               ("perl" ,perl-boot0)))

gnu/packages/patches/texinfo-headings-single.patch

@@ -0,0 +1,21 @@
+Fix a regression in 6.8 where the 'single' headings option was not recognized.
+
+Taken from upstream:
+
+  https://git.savannah.gnu.org/cgit/texinfo.git/commit/?id=13a8894fe2faa45b04033d7122a8fe7939ce6aa2
+
+diff --git a/tp/Texinfo/XS/parsetexi/end_line.c b/tp/Texinfo/XS/parsetexi/end_line.c
+index 4556780052..3fc2065616 100644
+--- a/tp/Texinfo/XS/parsetexi/end_line.c
++++ b/tp/Texinfo/XS/parsetexi/end_line.c
+@@ -778,8 +778,8 @@ kdbinputstyle_invalid:
+     case CM_headings:
+       {
+         if (!strcmp (line, "off") || !strcmp (line, "on")
+-            || !strcmp (line, "double") || !strcmp (line, "singleafter")
+-            || !strcmp (line, "doubleafter"))
++            || !strcmp (line, "single") || !strcmp (line, "double")
++            || !strcmp (line, "singleafter") || !strcmp (line, "doubleafter"))
+           {
+             ADD_ARG(line);
+           }

gnu/packages/texinfo.scm

@@ -52,6 +52,7 @@ (define-public texinfo
               (method url-fetch)
               (uri (string-append "mirror://gnu/texinfo/texinfo-"
                                   version ".tar.xz"))
+              (patches (search-patches "texinfo-headings-single.patch"))
               (sha256
                (base32
                 "1i7yb7mrp3inz25zbzv2pllr4y7d58v818f1as7iz8mw53nm7dwf"))))