[flags] Add an alias for opt => turbofan

This is temporary until we update our infra to always use --turbofan

Change-Id: Ie1ca8ce2cae6744515d9810ae4f57f00c8670e36
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3625977
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80355}

src/flags/flag-definitions.h

@@ -786,7 +786,10 @@ DEFINE_INT(deopt_every_n_times, 0,
 DEFINE_BOOL(print_deopt_stress, false, "print number of possible deopt points")
 
 // Flags for TurboFan.
-DEFINE_BOOL(turbofan, true, "use adaptive optimizations")
+DEFINE_BOOL(turbofan, true, "use the Turbofan optimizing compiler")
+// TODO(leszeks): Temporary alias until we make sure all our infra is passing
+// --turbofan instead of --opt.
+DEFINE_ALIAS_BOOL(opt, turbofan)
 
 DEFINE_BOOL(turbo_sp_frame_access, false,
             "use stack pointer-relative access to frame wherever possible")