Fix build
Fix build

cmake can't find FindLinuxPlatform.cmake.

I just googled and found a snippet that checks for distro-specific files
to set $PLATFORM that's pretty simple.

I'm not a cmake guru so if there's a better way then let me know :)

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

agrover/tcmu-runner,liuy/tcmu-runner,mkhon/tcmu-runner,superlibj/tcmu-runner,yasker/tcmu-runner,rancher/tcmu-runner,lxbsz/tcmu-runner,JefferyHu/tcmu-runner,open-iscsi/tcmu-runner,open-iscsi/tcmu-runner