More fixes for building x86 in Visual Studio for non-windows OS

[dgarske]

Description

More fixes for building x86 in Visual Studio for non-windows OS (Watcom C compiler). Followup to PR #7884. Fixes ZD 18465

• Consolidate the USE_WINDOWS_API to a single place.
• Expand the WOLFSSL_NOT_WINDOWS_API improvement for intrinsics and word sizes.
• Fix for macro variadic ... when no variables are used (some compilers like Watcom C have issue with this).
• Fix for Watcom C compiler "long long" -> "__int64".
• Fix a couple of minor cast warnings reported from VS.
• Fixes for consistency in SAVE_VECTOR_REGISTERS, ASSERT_SAVED_VECTOR_REGISTERS and RESTORE_VECTOR_REGISTERS.

Testing

Worked with customer

Checklist

• [ ] added tests
• [ ] updated/added doxygen
• [ ] updated appropriate READMEs
• [ ] Updated manual and documentation

[dgarske]

Stage 'PRB-medium-runtime.txt_4'
--enable-all --enable-asn=template --enable-dtls-mtu 
FAIL: scripts/openssl.test

[dgarske]

socat Tests:

FAILED: 146 216 309 310 326 386 399 402 459 460 467 468 478 492 528 530 FAILED unexpected: 326

[douzzer]

retest this please ("FAIL: scripts/external.test")