gnu: tcl: Fix cross-compilation.

* gnu/packages/patches/tcl-fix-cross-compilation.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/tcl.scm (tcl): Apply it.

gnu/local.mk

@@ -1383,6 +1383,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/tar-skip-unreliable-tests.patch		\
   %D%/packages/patches/tcc-boot-0.9.27.patch			\
   %D%/packages/patches/tclxml-3.2-install.patch			\
+  %D%/packages/patches/tcl-fix-cross-compilation.patch		\
   %D%/packages/patches/tcsh-fix-autotest.patch			\
   %D%/packages/patches/teensy-loader-cli-help.patch		\
   %D%/packages/patches/teeworlds-use-latest-wavpack.patch	\

gnu/packages/patches/tcl-fix-cross-compilation.patch

@@ -0,0 +1,39 @@
+From f7fa48c4c75a1e748dc5071e709c0b62ff739eaa Mon Sep 17 00:00:00 2001
+From: "jan.nijtmans" <nijtmans@users.sourceforge.net>
+Date: Mon, 9 Dec 2019 10:02:20 +0000
+Subject: [PATCH] Fix [abd4abedd2]: Failed to build tk 8.6.10 with cross
+ compile
+
+Patch taken from upstream to fix cross-compilation. To be removed on next Tcl release.
+
+---
+ compat/strtol.c  | 2 +-
+ compat/strtoul.c | 2 +-
+ 2 files changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/compat/strtol.c b/compat/strtol.c
+index b7f69196ce2..811006a64c3 100644
+--- a/compat/strtol.c
++++ b/compat/strtol.c
+@@ -53,7 +53,7 @@ strtol(
+      */
+ 
+     p = string;
+-    while (TclIsSpaceProc(*p)) {
++    while (isspace(UCHAR(*p))) {
+ 	p += 1;
+     }
+ 
+diff --git a/compat/strtoul.c b/compat/strtoul.c
+index e37eb05f823..15587f1da1a 100644
+--- a/compat/strtoul.c
++++ b/compat/strtoul.c
+@@ -74,7 +74,7 @@ strtoul(
+      */
+ 
+     p = string;
+-    while (TclIsSpaceProc(*p)) {
++    while (isspace(UCHAR(*p))) {
+ 	p += 1;
+     }
+     if (*p == '-') {

gnu/packages/tcl.scm

@@ -7,6 +7,7 @@
 ;;; Copyright © 2017 Kei Kebreau <kkebreau@posteo.net>
 ;;; Copyright © 2018 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2019 Julien Lepiller <julien@lepiller.eu>
+;;; Copyright © 2019 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -50,7 +51,8 @@
                                   version "/tcl" version "-src.tar.gz"))
               (sha256
                (base32
-                "1vc7imilx6kcb5319r7hnrp4jn5pqb41an3vr3azhgcfcgvdp5ji"))))
+                "1vc7imilx6kcb5319r7hnrp4jn5pqb41an3vr3azhgcfcgvdp5ji"))
+              (patches (search-patches "tcl-fix-cross-compilation.patch"))))
     (build-system gnu-build-system)
     (arguments
      `(#:phases (modify-phases %standard-phases