VectorMath: remove support for SSE1

Description

VectorMath_SSEx.c requires _mm_add_pd() which is an SSE2 intrinsic (defined in emmintrin.h) and therefore cannot be build on platforms with support for only SSE1 (e.g. at least some i386 systems).

Closes #211 (closed)

API Changes and Justification

Backwards Compatible Changes

• This change introduces no API changes
• This change adds new API calls

Backwards Incompatible Changes

• This change modifies an existing API
• This change removes an existing API

Review Status

N/A: build system changes only.