Use program_invocation_name instead of a local progname variable

Use program_invocation_name instead of a local progname variable

Emulate program_invocation_name only if it is not provided by libc.

* configure.ac: Check for program_invocation_name variable.
* strace.c (progname): Remove.
[!HAVE_PROGRAM_INVOCATION_NAME] (program_invocation_name): New variable.
(verror_msg, error_msg_and_help): Use it instead of progname.
(init): Initialize program_invocation_name instead of progname.