perf symbols: Add mwait_idle_with_hints.constprop.0 to the list of idle symbols

The "mwait_idle_with_hints" one was already there, some compiler
artifact now adds this ".constprop.0" suffix, cover that one too.

At some point we need to put these in a special bucket and show it
somewhere on the screen.

Noticed building the kernel on a fedora:32 system using:

gcc version 10.2.1 20200723 (Red Hat 10.2.1-1) (GCC)

Cc: Adrian Hunter <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/symbol.c

···
 		"exit_idle",
 		"mwait_idle",
 		"mwait_idle_with_hints",
+		"mwait_idle_with_hints.constprop.0",
 		"poll_idle",
 		"ppc64_runlatch_off",
 		"pseries_dedicated_idle_sleep",