[libxml2] Disable pointer-overflow UBSan checks under Travis

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 1637d612d15318496804d59fc92594d732c5258a
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Jan 8 19:19:42 2018 +0100

    Disable pointer-overflow UBSan checks under Travis
    
    clang 5 added UBSan checks for pointer overflow which are triggered by
    an API test.

 .travis.yml |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/.travis.yml b/.travis.yml
index 3ad04c8..da48143 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,7 +15,7 @@ matrix:
     - compiler: clang
       dist: trusty
       env: CONFIG="--without-python"
-           CFLAGS="-O2 -g -fno-omit-frame-pointer -fsanitize=address,undefined 
-fno-sanitize=float-divide-by-zero -fno-sanitize-recover=all -Werror -Wno-error=unused-function 
-Wno-error=cast-align"
+           CFLAGS="-O2 -g -fno-omit-frame-pointer -fsanitize=address,undefined 
-fno-sanitize=float-divide-by-zero,pointer-overflow -fno-sanitize-recover=all -Werror 
-Wno-error=unused-function -Wno-error=cast-align"
            UBSAN_OPTIONS=print_stacktrace=1
 script: sh autogen.sh $CONFIG && make -j2 V=1 && make check
 git: