perf tools: Handle -h and -v options

Adding handling for '-h' and '-v' options to invoke help and version
command respectively.

Current behaviour is:

$ perf -v
Unknown option: -v

Usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]
$ perf -h
Unknown option: -h

Usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

New behaviour:

$ perf -h

usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

The most commonly used perf commands are:
annotate Read perf.data (created by perf record) and display annotated code
archive Create archive with object files with build-ids found in perf.data file
bench General framework for benchmark suites
...

$ perf -v
perf version 4.3.rc3.gc99e32

Updated man page.

Requested-by: Peter Zijlstra <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Don Zickus <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf.txt

···
 	Setup buildid cache directory. It has higher priority than
 	buildid.dir config file option.
 
+-v::
+--version::
+  Display perf version.
+
+-h::
+--help::
+  Run perf help command.
+
 DESCRIPTION
 -----------
 Performance counters for Linux are a new kernel-based subsystem

tools/perf/perf.c

···
 			break;
 
 		/*
+		 * Shortcut for '-h' and '-v' options to invoke help
+		 * and version command.
+		 */
+		if (!strcmp(cmd, "-h")) {
+			(*argv)[0] = "--help";
+			break;
+		}
+
+		if (!strcmp(cmd, "-v")) {
+			(*argv)[0] = "--version";
+			break;
+		}
+
+		/*
 		 * Check remaining flags.
 		 */
 		if (!prefixcmp(cmd, CMD_EXEC_PATH)) {