Improve compiler flags for warnings and disable -Wstringop-foo warnings

[nstoddard]

This brings the warnings produced by GCC closer to those produced by clang. Clang still generates a few warnings that GCC doesn't seem to support, however.

This also disables -Wstringop-truncation, -overread, and -overflow, since the resulting warnings are probably useless. Clang doesn't support those flags, so this unfortunately has to be done with #pragmas in Rogue.h.

I recommend not merging this until #789 is merged, because that PR fixes dozens of warnings that currently only show up in Clang, and this PR will enable those warnings in GCC.

[tmewett]

I don't understand the disabling in the header file thing.. are the -Wstringop-* warnings coming from an umbrella -W? Won't compilers just ignore a -W that they don't understand?

[nstoddard]

I don't understand the disabling in the header file thing.. are the -Wstringop-* warnings coming from an umbrella -W? Won't compilers just ignore a -W that they don't understand?

The stringop warnings seem to be enabled by default in GCC. And unfortunately Clang does not ignore unknown warning flags; instead it prints the following for every single file:

warning: unknown warning option '-Wstringop-truncation'; did you mean '-Wformat-truncation'? [-Wunknown-warning-option]
warning: unknown warning option '-Wstringop-overread' [-Wunknown-warning-option]
warning: unknown warning option '-Wstringop-overflow'; did you mean '-Wshift-overflow'? [-Wunknown-warning-option]

From those messages, you'd think we could just add -Wno-unknown-warning-option to the Makefile. And that does in fact get rid of these warnings in Clang. But unfortunately, doing so causes GCC to print a bunch of the following:

cc1: note: unrecognized command-line option ‘-Wno-unknown-warning-option’ may have been intended to silence earlier diagnostics

Also, using a #pragma to ignore -Wunknown-warning-option in Clang doesn't seem to work, for some reason.

Not sure what the compiler developers were thinking here. Unfortunately I don't see a less ugly way to handle this.

[tmewett]

instead it prints the following for every single file

I don't understand why clang is printing a warning for a flag that doesn't appear on the command line 🤔

[nstoddard]

instead it prints the following for every single file

I don't understand why clang is printing a warning for a flag that doesn't appear on the command line 🤔

Oops, I edited the Makefile incorrectly for that particular test (I accidentally included -Wstringop-truncation instead of -Wno-stringop-truncation etc). But if the Makefile includes -Wno-stringop-truncation -Wno-stringop-overread -Wno-stringop-overflow, it still prints lines like warning: unknown warning option '-Wno-stringop-truncation'; did you mean '-Wno-format-truncation'? [-Wunknown-warning-option].

If these warning flags are disabled using #pragmas instead of in the Makefile, no such messages are printed.

[tmewett]

Ok, I think this makes sense, let's do it. I'll merge when the conflicts are fixed

[nstoddard]

I fixed the merge conflicts. I sorted the warning flags a bit differently than before (e.g. grouping together prototype-related flags instead of grouping together all -Werror=foo flags). I have a slight preference for organizing them like this, but let me know if I should change it to be more similar to how it was.