Add option to force generic algorithms on x86 (#22917)
Option is named onnxruntime_FORCE_GENERIC_ALGORITHMS
Follow up to https://github.com/microsoft/onnxruntime/pull/22125.
### Description
This change adds compile-time option to disable optimized algorithms and
use generic algorithms (exclude AVX* and SSE etc in GEMM) on x86. This
new option is intended only for testing these algorithms, not for
production use.
Following build command on linux x86_64 builds onnxruntime with new
option enabled:
`./build.sh --parallel --cmake_extra_defines
onnxruntime_FORCE_GENERIC_ALGORITHMS=1`
### Motivation and Context
This change allows testing generic algorithms. This may be needed for
platforms which don't have optimized implementations available, like in
https://github.com/microsoft/onnxruntime/pull/22125.
