Remove SEGV_MTEAERR check.

SEGV_MTEARR/SEGV_MTESERR are always defined now, so no need to
check before using them.

Add the signal.h include so that this actually works properly.

Test: Builds/Treehugger
Change-Id: Iec6e7c69cd80a002ea972f32834bdc6701af5063