Silence gcc new/delete warnings for texturesys

[Shootfast]

Description

Disable GCC warnings around mismatched new/delete for shared_texturesys creation

Tests

Checklist:

• I have read the contribution guidelines.
• If this is more extensive than a small change to existing code, I
  have previously submitted a Contributor License Agreement
  (individual, and if there is any way my
  employers might think my programming belongs to them, then also
  corporate).
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite
  (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[lgritz]

We have macros defined in platform.h for these things. In the parlance we use through the rest of the code base, this would be

OIIO_PRAGMA_WARNING_PUSH
#if OIIO_GNUC_VERSION > 100000
    OIIO_GCC_ONLY_PRAGMA(diagnostic ignored "-Wmismatched-new-delete")
#endif
...
OIIO_PRAGMA_WARNING_POP

I admit that for this small example, this is not especially any more clear than the raw pragmas you used. But the point is that it'll always work properly, no future non-gcc compiler will complain about those GCC pragma (which I am kinda superstitious about, even though CI shows it appears to be fine on the compilers we test).

[Shootfast]

Awesome, I've updated the pull request to use the existing macros.
I also edited the comment as this now only applies to GCC (as your macros explicitly single out that compiler). Usually clang respects gcc pragmas, but I don't have a clang toolchain easily available, and I guess the existing CI builders haven't complained so far

[lgritz]

I took the liberty of pushing a fix to the clang-format CI complaints. If this passes CI, I will merge.

[Shootfast]

One day I will remember to run the clang-format pass first 😅

[lgritz]

No prob. It was tricky in this case because I guess clang-format is ok with the #if and #pragma being in the first column, so it passed clang-format your first time through. But after changing to the macros as I suggested, clang-format thought it should be indented like regular code, and started complaining.

One day I (or hopefully somebody else?) will figure out how to do a special GitHub action that will take a failed CI clang-format test and automatically turn it into an appended comment on the PR with the suggested diff of changes that can be merged in a single click. Actually, it appears there are a number of such implementations in the GitHub Action marketplace, the main task is probably to figure out which one suits our needs.