perf check: Allow showing a tip for opt-in features not built into perf

Ingo reported that it was difficult to understand why libunwind support
didn't link even when he had the usual libunwind-dev files installed in
his machine.

This is because libunwind became opt-in, the user has to use
LIBUNWIND=1, as it was deemed stalled in its development/unsuitable for
use with perf, IIRC, and so we better use the elfutils equivalent
routine that we also supported for ages.

But the build message still printed:

Auto-detecting system features:
... libdw: [ on ]
... glibc: [ on ]
<SNIP>
... libcrypto: [ on ]
... libunwind: [ OFF ]
<SNIP>

Which is confusing, so allow for having a tip when 'perf version
--build-options' is used, and variants with 'perf check feature':

$ perf version --build-options | grep libunwind
libunwind: [ OFF ] # HAVE_LIBUNWIND_SUPPORT ( tip: Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it )
$
$ perf check feature libunwind
libunwind: [ OFF ] # HAVE_LIBUNWIND_SUPPORT ( tip: Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it )
$

The next patches will remove the opt-in libunwind FEATURES_DISPLAY.

Reported-by: Ingo Molnar <[e-mail]>
Tested-by: Ingo Molnar <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Dmitriy Vyukov <[e-mail]>
Cc: Howard Chu <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-check.c

···
 	.macro = #macro_,                  \
 	.is_builtin = IS_BUILTIN(macro_) }
 
+#define FEATURE_STATUS_TIP(name_, macro_, tip_) { \
+	.name = name_,				  \
+	.macro = #macro_,			  \
+	.tip = tip_,				  \
+	.is_builtin = IS_BUILTIN(macro_) }
+
 struct feature_status supported_features[] = {
 	FEATURE_STATUS("aio", HAVE_AIO_SUPPORT),
 	FEATURE_STATUS("bpf", HAVE_LIBBPF_SUPPORT),
···
 	FEATURE_STATUS("libpython", HAVE_LIBPYTHON_SUPPORT),
 	FEATURE_STATUS("libslang", HAVE_SLANG_SUPPORT),
 	FEATURE_STATUS("libtraceevent", HAVE_LIBTRACEEVENT),
-	FEATURE_STATUS("libunwind", HAVE_LIBUNWIND_SUPPORT),
+	FEATURE_STATUS_TIP("libunwind", HAVE_LIBUNWIND_SUPPORT, "Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it"),
 	FEATURE_STATUS("lzma", HAVE_LZMA_SUPPORT),
 	FEATURE_STATUS("numa_num_possible_cpus", HAVE_LIBNUMA_SUPPORT),
 	FEATURE_STATUS("zlib", HAVE_ZLIB_SUPPORT),
···
 
 	printf("%22s: ", name);
 	on_off_print(status);
-	printf("  # %s\n", macro);
+	printf("  # %s", macro);
+
+	if (!feature->is_builtin && feature->tip)
+		printf(" ( tip: %s )", feature->tip);
+
+	putchar('\n');
 }
 
 /**

tools/perf/builtin.h

···
 struct feature_status {
 	const char *name;
 	const char *macro;
+	const char *tip;
 	int is_builtin;
 };