RFR: 8243208: Clean up JVMFlag implementation [v3]

[Ioi Lam]

On Wed, 9 Sep 2020 14:13:15 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed JVMFlag::is_writeable()
>
> src/hotspot/share/runtime/flags/jvmFlagLookup.hpp line 44:
> 
>> 42:     }
>> 43:     return h;
>> 44:   }
> 
> Can this function just call hash_code(s, strlen(s)) ?

strlen() is not constexpr so it can't be used here. I added my hand-rolled string_len function in
[bf90a37](https://github.com/openjdk/jdk/pull/82/commits/bf90a3765720267a8770f7bb0cc6957471ccb21b) so we can share a
single copy of the hash calculation loop.

-------------

PR: https://git.openjdk.java.net/jdk/pull/82