[XXS] C1 misses to dump a reason when it inlines successfully

[Liu Xin]

hi, Reviewers,

Could you review this extremely small change?
Bugs: https://bugs.openjdk.java.net/browse/JDK-8234541
Webrev: https://cr.openjdk.java.net/~xliu/8234541/00/webrev/

When I analyzed PrintInlining, I was confused by the inline message without
any detail. It's not easy for developer to tell if this method is inlined
or not. This patch add a comment "inline by the rules of C1".

I would like to add an explicit reason, but there's no decisive reason in
GraphBuilder::try_inline_full. It just passes all restrict rules. Any other
suggestion would be appreciated.

Thanks,
--lx