Add some supporting framework for C11-style atomics.

Uses the stdatomic.h provided by FreeBSD when GCC doesn't (ie. GCC < 4.9)

Signed-off-by: Jonathon Anderson <jma14@rice.edu>
Signed-off-by: Srđan Milaković <sm108@rice.edu>
diff --git a/lib/Makefile.am b/lib/Makefile.am
index 36d21a0..3086cf0 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -38,7 +38,8 @@
 		  color.c printversion.c
 
 noinst_HEADERS = fixedsizehash.h libeu.h system.h dynamicsizehash.h list.h \
-		 eu-config.h color.h printversion.h bpf.h
+		 eu-config.h color.h printversion.h bpf.h \
+		 atomics.h stdatomic-fbsd.h
 EXTRA_DIST = dynamicsizehash.c
 
 if !GPROF