Exclude BFloat16 CPU kernels from WebAssembly builds
WebAssembly does not support bfloat16 types natively. This commit adds
preprocessor guards (__wasm__ and __EMSCRIPTEN__) to exclude BFloat16
Gemm and MatMul kernels from WebAssembly builds.
Changes:
- Guard BFloat16 kernel declarations in cpu_execution_provider.cc
- Guard BFloat16 kernel registrations in cpu_execution_provider.cc
- Guard BFloat16 Gemm kernel and implementation in gemm.cc
- Guard BFloat16 MatMul kernel in matmul.cc
- Guard BFloat16 Gemm and MatMul implementations in math_cpu.cc
This follows the existing pattern used throughout the codebase for
WebAssembly-specific code exclusion (see profiler.h, threadpool.cc, etc.)
and prevents build failures when compiling for WebAssembly platforms.
