Auto merge of rust-lang#135439 - clubby789:O3, r=<try>

[EXPERIMENTAL] Make `-O` mean `OptLevel::Aggressive`

Just out of curiosity to see if anything is relying on this

r? ghost

Author: bors

compiler/rustc_session/src/config.rs

@@ -2097,7 +2097,7 @@ fn parse_opt_level(
         })
         .max();
     if max_o > max_c {
-        OptLevel::Default
+        OptLevel::Aggressive
     } else {
         match cg.opt_level.as_ref() {
             "0" => OptLevel::No,