Enable building valgrind on host with 4.x kernel.

For OpenEmbedded builds we should be checking something like
OLDEST_KERNEL instead of `uname -r`, but this is good enough for now.

Building on 4.x* currently fails with:
  configure:5556: checking for the kernel version
  configure:5579: result: unsupported (4.0.0-rc3-00111-gaffb817)
  configure:5581: error: Valgrind works on kernels 2.4, 2.6

Upstream-Status: Pending
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

--- valgrind-3.9.0/configure.ac.orig	2015-03-13 19:17:01.247310868 +0100
+++ valgrind-3.9.0/configure.ac	2015-03-13 19:19:27.388316108 +0100
@@ -276,9 +276,9 @@
         kernel=`uname -r`
 
         case "${kernel}" in
-             2.6.*|3.*) 
-        	    AC_MSG_RESULT([2.6.x/3.x family (${kernel})])
-        	    AC_DEFINE([KERNEL_2_6], 1, [Define to 1 if you're using Linux 2.6.x or Linux 3.x])
+             2.6.*|3.*|4.*) 
+        	    AC_MSG_RESULT([2.6.x/3.x/4.x family (${kernel})])
+        	    AC_DEFINE([KERNEL_2_6], 1, [Define to 1 if you're using Linux 2.6.x or Linux 3.x or Linux 4.x])
         	    ;;
 
              2.4.*) 
@@ -288,7 +288,7 @@
 
              *) 
         	    AC_MSG_RESULT([unsupported (${kernel})])
-        	    AC_MSG_ERROR([Valgrind works on kernels 2.4, 2.6])
+        	    AC_MSG_ERROR([Valgrind works on kernels 2.4, 2.6, 3.x, 4.x])
         	    ;;
         esac