Include string.h as strerror depends on it

The host build of trout AGL services is broken because strerror
is undefined. The header string.h does bring in this function, so
adding it is sufficient to fix the issue

Bug: 183028968
Test: build.sh in lv-docker utils
Change-Id: I8e3a0ddd93f90e8475673a4303d75958635381c3
1 file changed