libtinyxml2: drop trailing continuation character in do_compile

* with newer bitbake it parses it differently and task fails:
  http://errors.yoctoproject.org/Errors/Details/35147/


  DEBUG: Executing shell function do_compile
  /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/libtinyxml2/2.2.0+gitAUTOINC+d211bb1351-r0/temp/run.do_compile.21186: 118: /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/libtinyxml2/2.2.0+gitAUTOINC+d211bb1351-r0/temp/run.do_compile.21186: Syntax error: end of file unexpected (expecting "}")
  WARNING: exit code 2 from a shell command.
  ERROR: Function failed: do_compile (log file is located at /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/libtinyxml2/2.2.0+gitAUTOINC+d211bb1351-r0/temp/log.do_compile.21186)

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