Lower optimization level workaround for omrzfs.c

[Deigue]

Lowering the optimization level is the workaround considered for compiling omrzfs.c with Open XL support, until a permanent solution or fix is made. Compiling with -O3 currently causes a crash using Open XL.

[babsingh]

Using -O0 will result in significant performance regression. There should be separate documentation on the -O3 crash, tracked in a dedicated issue. This PR should be linked to that issue so it can be reverted once the -O3 crash is resolved. Additionally, have you explored modifying the source code in omrzfs.c to address the -O3 crash?

[babsingh]

@joransiu What are your thoughts on this PR?

[Deigue]

I have attempted to but unable to address it. Admittedly, I guess I can wrap the lowering of the optimization level restricted only to when using the Open XL compiler with (#define(__open_xl__)) so as to only really do this when absolutely necessary. That way I guess we won't be impacting all the ZOS instances.

[joransiu]

To mitigate the performance impact, we can try to add __attribute__((optnone)) to the problematic function that Open XL has issues with: https://www.ibm.com/docs/en/open-xl-c-cpp-zos/2.1?topic=pragmas-pragma-option-override