flex: fix build with autoconf 2.70

autoconf 2.70 is coming soon which has some small behavioural fixes, so
backport a patch from upstream to fix the build with that release.

(From OE-Core rev: 946610f2cc8cd42265ee3fab6c73ad4831aaeb4e)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/flex/flex/check-funcs.patch

@@ -0,0 +1,79 @@
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+
+From c42de062bbdc7c31d7181c10a74202d493280ada Mon Sep 17 00:00:00 2001
+From: Explorer09 <explorer09@gmail.com>
+Date: Tue, 27 Feb 2018 09:10:12 +0800
+Subject: [PATCH] build: Move dnl comments out of AC_CHECK_FUNCS
+
+Due to a bug, autoheader (2.69) will treat M4 dnl comments in a quoted
+argument of AC_CHECK_FUNCS as function tokens and generate a lot of
+redundant and useless HAVE_* macros in config.h.in.
+(Examples: HAVE_DNL, HAVE_AVAILABLE_, HAVE_BY)
+
+It seems to be this commit dbb4e94dc7bacbcfd4acef4f085ef752fe1aa03f of
+mine that revealed this autoheader bug, and the affected config.h.in
+had been shipped within flex-2.6.4 release tarball.
+
+I have reported the autoheader bug here:
+<https://lists.gnu.org/archive/html/bug-autoconf/2018-02/msg00005.html>
+
+As a workaround, let's move comments out of AC_CHECK_FUNCS.
+
+Signed-off-by: Kang-Che Sung <explorer09@gmail.com>
+---
+ configure.ac | 29 +++++++++++++----------------
+ 1 file changed, 13 insertions(+), 16 deletions(-)
+
+diff --git a/configure.ac b/configure.ac
+index 55e774b0..d0f3b7da 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -166,6 +166,7 @@ strtol dnl
+ AC_CHECK_FUNCS([dnl
+ pow dnl           Used only by "examples/manual/expr"
+ setlocale dnl     Needed only if NLS is enabled
++reallocarr dnl    NetBSD function. Use reallocarray if not available.
+ reallocarray dnl  OpenBSD function. We have replacement if not available.
+ ])
+ 
+diff --git a/configure.ac b/configure.ac
+index 3c977a4e..9c53590f 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -158,22 +158,19 @@ AC_FUNC_REALLOC
+ AS_IF([test "$cross_compiling" = yes],
+    AC_MSG_WARN([result $ac_cv_func_realloc_0_nonnull guessed because of cross compilation]))
+ 
+-AC_CHECK_FUNCS([dup2 dnl
+-memset dnl
+-regcomp dnl
+-strcasecmp dnl
+-strchr dnl
+-strdup dnl
+-strtol dnl
+-], [], [AC_MSG_ERROR(required library function not found on your system)])
+-
+-# Optional library functions
+-AC_CHECK_FUNCS([dnl
+-pow dnl           Used only by "examples/manual/expr"
+-setlocale dnl     Needed only if NLS is enabled
+-reallocarr dnl    NetBSD function. Use reallocarray if not available.
+-reallocarray dnl  OpenBSD function. We have replacement if not available.
+-])
++dnl Autoheader (<= 2.69) bug: "dnl" comments in a quoted argument of
++dnl AC_CHECK_FUNCS will expand wierdly in config.h.in.
++dnl (https://lists.gnu.org/archive/html/bug-autoconf/2018-02/msg00005.html)
++
++AC_CHECK_FUNCS([dup2 memset regcomp strcasecmp strchr strdup strtol], [],
++  [AC_MSG_ERROR(required library function not found on your system)])
++
++# Optional library functions:
++# pow - Used only by "examples/manual/expr".
++# setlocale - Needed only if NLS is enabled.
++# reallocarr - NetBSD function. Use reallocarray if not available.
++# reallocarray - OpenBSD function. We have replacement if not available.
++AC_CHECK_FUNCS([pow setlocale reallocarr reallocarray])
+ 
+ AC_CONFIG_FILES(
+ Makefile

meta/recipes-devtools/flex/flex_2.6.4.bb

@@ -15,6 +15,7 @@ SRC_URI = "https://github.com/westes/flex/releases/download/v${PV}/flex-${PV}.ta
            file://0001-tests-add-a-target-for-building-tests-without-runnin.patch \
            ${@bb.utils.contains('PTEST_ENABLED', '1', '', 'file://disable-tests.patch', d)} \
            file://0001-build-AC_USE_SYSTEM_EXTENSIONS-in-configure.ac.patch \
+           file://check-funcs.patch \
            "
 
 SRC_URI[md5sum] = "2882e3179748cc9f9c23ec593d6adc8d"