Implement decoding of fsconfig syscall

Implement decoding of fsconfig syscall

... introduced by Linux kernel commits v5.2-rc1~141^2~3,
v5.2-rc1~20^2~1, and v5.2-rc1~20^2.

* fsconfig.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* pathtrace.c (pathtrace_match_set): Add SEN_fsconfig.
* xlat/fsconfig_cmds.in: New file.
* linux/syscallent-common.h [BASE_NR + 431]: Wire up fsconfig.
* NEWS: Mention this change.
* tests/fsconfig.c: New file.
* tests/fsconfig-P.c: Likewise.
* tests/gen_tests.in (fsconfig, fsconfig-P): New entries.
* tests/pure_executables.list: Add fsconfig and fsconfig-P.
* tests/.gitignore: Likewise.