[makefile] Modify makefile to be compatible.

Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
Fuck GNU.
[onchange] Remove error pragma on BSDs, compile nicely.

Gcc doesn't like strcat though.
Use feature macros, now compiles with -std=c99.
Merge branch 'master' into oc-kevent
Merge branch 'master' into oc-kevent
Merge branch 'oc-kevent' of github.com:cadadr/dumbtools-c into oc-kevent
[onchange] Implement kevent support.
Merge branch 'master' of github.com:cadadr/dumbtools-c
[common.h] ERRNO_OUT: Tell progname.
Merge branch 'oc-kevent'