perf build: Add missing comment about NO_LIBTRACEEVENT=1

By default perf will fail the build if the development files for
libtraceevent are not available.

To build perf without libtraceevent support, disabling several features
such as 'perf trace', one needs to add NO_LIBTRACEVENT=1 to the make
command line.

Add the missing comments about that to the tools/perf/Makefile.perf
file, just like all the other such command line toggles.

Fixes: 378ef0f5 ("perf build: Use libtraceevent from the system")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/ZR6+MhXtLnv6ow6E@kernel.orgSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/Makefile.perf

@@ -69,6 +69,10 @@ include ../scripts/utilities.mak
 # Define NO_LIBDW_DWARF_UNWIND if you do not want libdw support
 # for dwarf backtrace post unwind.
 #
+# Define NO_LIBTRACEEVENT=1 if you don't want libtraceevent to be linked,
+# this will remove multiple features and tools, such as 'perf trace',
+# that need it to read tracefs event format files, etc.
+#
 # Define NO_PERF_READ_VDSO32 if you do not want to build perf-read-vdso32
 # for reading the 32-bit compatibility VDSO in 64-bit mode
 #