ilmbase, openexr: update to 2.5.5

## Version 2.5.5 (February 12, 2021)

Patch release with various bug/sanitizer/security fixes, primarily
related to reading corrupted input files, but also a fix for universal
build support on macOS.

Specific OSS-fuzz issues include:

* OSS-fuzz [#30291](https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30291)
* OSS-fuzz [#29106](https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29106)
* OSS-fuzz [#28971](https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28971)
* OSS-fuzz [#29829](https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29829)
* OSS-fuzz [#30121](https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30121)

### Merged Pull Requests

* [#914](https://github.com/AcademySoftwareFoundation/openexr/pull/914) additional verification of DWA data sizes
* [#910](https://github.com/AcademySoftwareFoundation/openexr/pull/910) update tileoffset sanitycheck to handle ripmaps
* [#903](https://github.com/AcademySoftwareFoundation/openexr/pull/903) prevent overflows by using Int64 for all vars in DWA initialize
* [#901](https://github.com/AcademySoftwareFoundation/openexr/pull/901) Use size_t for DWA buffersize calculation
* [#897](https://github.com/AcademySoftwareFoundation/openexr/pull/897) prevent overflow in RgbaFile cachePadding
* [#896](https://github.com/AcademySoftwareFoundation/openexr/pull/896) add buffer size validation to FastHuf decode
* [#893](https://github.com/AcademySoftwareFoundation/openexr/pull/893) Include <limits> where required by newer compilers
* [#889](https://github.com/AcademySoftwareFoundation/openexr/pull/889) Add explicit #include <limits> for numeric_limits
* [#854](https://github.com/AcademySoftwareFoundation/openexr/pull/854) Fix Apple Universal 2 (arm64/x86_64) builds

(wiz)