libelf-0.8.13: Fix libelf 64bit detection

Taken from crosstool-ng and and re-applied to 0.8.13

diff -urN libelf-0.8.13.orig/configure libelf-0.8.13/configure
--- libelf-0.8.13.orig/configure	2008-05-23 01:18:03.000000000 -0700
+++ libelf-0.8.13/configure	2017-07-27 12:41:43.417835628 -0700
@@ -1595,7 +1595,7 @@
   echo $ac_n "(cached) $ac_c" 1>&6
 else
   if test "$cross_compiling" = yes; then
-  ac_cv_sizeof_long_long=0
+  ac_cv_sizeof_long_long=8
 else
   cat > conftest.$ac_ext <<EOF
 #line 1602 "configure"
diff -urN libelf-0.8.13.orig/configure.in libelf-0.8.13/configure.in
--- libelf-0.8.13.orig/configure.in	2008-05-23 01:17:56.000000000 -0700
+++ libelf-0.8.13/configure.in	2017-07-27 12:41:43.421835676 -0700
@@ -90,7 +90,7 @@
 AC_CHECK_SIZEOF(short,2)
 AC_CHECK_SIZEOF(int,4)
 AC_CHECK_SIZEOF(long,4)
-AC_CHECK_SIZEOF(long long,0)
+AC_CHECK_SIZEOF(long long,8)
 # Windows port
 AC_CHECK_SIZEOF(__int64, 0)