Fix the clobbering of an XMM register on Windows in sha256_one_block_avx

[hanblee]

Description

The size of _XMM_SAVE was incorrectly set to 7. This PR changes it to 8.

Affected parts

• [x] Library
• [ ] Test Application
• [ ] Perf Application
• [ ] Other: (please specify)

Motivation and Context

On Windows, the stack space for the last (%RSP+0x70) gets clobbered and when the clobbered data gets restored to XMM register, it also gets garbage data.

How Has This Been Tested?

An internal test app which was failing now passes.

Windows using MinGW/gcc

It should not.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

[pablodelara]

Code has been merged separately. Thanks!