process.c: move prctl and arch_prctl parsers to a separate file

* prctl.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* process.c: Move sys_prctl, sys_arch_prctl, and related code to prctl.c.
diff --git a/Makefile.am b/Makefile.am
index cd097a4..2f5a8bf 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -55,6 +55,7 @@
 	or1k_atomic.c	\
 	pathtrace.c	\
 	personality.c	\
+	prctl.c		\
 	printmode.c	\
 	process.c	\
 	process_vm.c	\