Dear Maintainer,

tboot is failing to build in Ubuntu with the error:

<command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]

This is because tboot source adds -D_FORTIFY_SOURCE=2 while building, and
Ubuntu is adding -D_FORTIFY_SOURCE=3 to the buildflags and so a redefinition.

The problem is not seen in Debian as Debian also builds with -D_FORTIFY_SOURCE=2

The attched patch is going to fix the problem, it will check if -D_FORTIFY_SOURCE
is in the CFLAGLS or CPPFLGS or not and will -D_FORTIFY_SOURCE=2 if its not present.

It will be really appreciated if the patch can be added.
Thanks in advance.