[source] tools: flex: fix build with automake 1.15.1

[LEDE Commits]

jow pushed a commit to source.git, branch master:
https://git.lede-project.org/91e262c6b35a748c743607da2d3ead4764e05038

commit 91e262c6b35a748c743607da2d3ead4764e05038
Author: Jo-Philipp Wich <jo at mein.io>
AuthorDate: Wed Jul 5 19:19:30 2017 +0200

    tools: flex: fix build with automake 1.15.1
    
    After the update of GNU automake, the flex configure fails with
    
        configure.ac:31: error: version mismatch.  This is Automake 1.15.1,
        configure.ac:31: but the definition used by this AM_INIT_AUTOMAKE
        configure.ac:31: comes from Automake 1.15.
    
    Apply the autoreconf host fixup to properly regenerate configure before
    to avoid triggering the version mismatch. Also refresh the patch while
    we're at it.
    
    Fixes FS#885.
    
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 tools/flex/Makefile                             | 1 +
 tools/flex/patches/100-disable-tests-docs.patch | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/flex/Makefile b/tools/flex/Makefile
index 760721a..1398b1a 100644
--- a/tools/flex/Makefile
+++ b/tools/flex/Makefile
@@ -13,6 +13,7 @@ PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://github.com/westes/flex/releases/download/v$(PKG_VERSION)/
 PKG_HASH:=e87aae032bf07c26f85ac0ed3250998c37621d95f8bd748b31f15b33c45ee995
 
+HOST_FIXUP:=autoreconf
 HOST_BUILD_PARALLEL:=1
 
 include $(INCLUDE_DIR)/host-build.mk
diff --git a/tools/flex/patches/100-disable-tests-docs.patch b/tools/flex/patches/100-disable-tests-docs.patch
index f298bc9..f7097f2 100644
--- a/tools/flex/patches/100-disable-tests-docs.patch
+++ b/tools/flex/patches/100-disable-tests-docs.patch
@@ -1,8 +1,8 @@
 --- a/Makefile.am
 +++ b/Makefile.am
-@@ -45,10 +45,7 @@ EXTRA_DIST = \
+@@ -43,10 +43,7 @@ EXTRA_DIST = \
+ 
  SUBDIRS = \
- 	lib \
  	src \
 -	doc \
 -	examples \