process.c: move futex parser to a separate file

* futex.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* process.c: Move sys_futex and related code to futex.c.
diff --git a/Makefile.am b/Makefile.am
index 917e08c..9342123 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -34,6 +34,7 @@
 	fallocate.c	\
 	fanotify.c	\
 	file.c		\
+	futex.c		\
 	get_robust_list.c \
 	getcpu.c	\
 	getcwd.c	\