devel/m4: upgrade to release 1.4.18

NEWS has these comments:

Noteworthy changes in release 1.4.18 (2016-12-31) [stable]
* Diagnose --word-regexp as unsupported if it was not configured.
* Preliminary support for OS/2.
* A number of portability improvements inherited from gnulib.

SHA256SUM is used as package checksum

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

devel/m4/Makefile

@@ -8,12 +8,12 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=m4
-PKG_VERSION:=1.4.17
-PKG_RELEASE:=2
+PKG_VERSION:=1.4.18
+PKG_RELEASE:=1
 
 PKG_SOURCE_URL:=@GNU/m4
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
-PKG_MD5SUM:=12a3c829301a4fd6586a57d3fcf196dc
+PKG_MD5SUM:=f2c1e86ca0a404ff281631bdc8377638992744b175afb806e25871a24a934e07
 PKG_MAINTAINER:=Heinrich Schuchardt <xypron.glpk@gmx.de>
 PKG_LICENSE:=GPL-3.0+