signal.c: move siginfo_t parsers to a separate file

* printsiginfo.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* defs.h (printsiginfo): Change second argument's type from int to bool.
* signal.c: Stop defining siginfo_t related constants.
Move inclusion of xlat/sig*_codes.h files to printsiginfo.c
(printsigsource, printsigval, printsiginfo_at): Move to printsiginfo.c.
(printsiginfo): Change second argument's type from int to bool,
split, and move to printsiginfo.c.
diff --git a/Makefile.am b/Makefile.am
index c4c0138..8193c9e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -77,6 +77,7 @@
 	personality.c	\
 	prctl.c		\
 	printmode.c	\
+	printsiginfo.c	\
 	printstat.h	\
 	process.c	\
 	process_vm.c	\