Proposal: adding --enable-shadows-warning

Hi Hackers,

I had an experience where I made a patch ready locally, build passed without any warning, however, CommitFest CI failed
witha compile waring of shadows variable. I felt strange at the time but now I understand that is because some
compilers,like clang I am using, don’t enable -Wshadow by default. So obviously the CommitFest CI has enabled -Wshadow.
Sucha situation is kinda wasting patch author’s time. 

To make hacker’s life easier, it would make sense to always enable “-Wshadow”, however, that may have a risk of
breakingsome compilers. So thinking over, I just fell adding an opt-in “—enable-shadows-warnings” could be a solution.  

Before the option is added “./confgure”, a workaround is like: PROFILE=“-Wshadow” make, but that way is just a
workaround,it’s easy to forget use the extra thing together with make. 

I have tried to add the option locally, but end up I gave up because of the issue I posted in a separate thread [1].
Once[1] is resolved and if no objection on this proposal, then I will be happy to create a patch to add this option. 

[1] https://postgr.es/m/913843DF-16BA-4241-8191-BF892049744A@gmail.com

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/