onnxruntime

Enable RISC-V 64-bit Cross-Compiling Support for ONNX Runtime on Linux (#19238)

### Description  
This pull request introduces the necessary changes to enable RISC-V
64-bit cross-compiling support for the ONNX Runtime on Linux. The RISC-V
architecture has gained popularity as an open standard instruction set
architecture, and this contribution aims to extend ONNX Runtime's
compatibility to include RISC-V, thereby broadening the reach of ONNX
models to a wider range of devices.

### Motivation and Context
RISC-V is a free and open-source instruction set architecture (ISA)
based on established RISC principles. It is provided under open licenses
without fees. Due to its extensibility and freedom in both software and
hardware, RISC-V is poised for widespread adoption in the future,
especially in applications related to AI, parallel computing, and data
centers.

### Example Build Command
```
./build.sh --parallel --config Debug --rv64 --riscv_toolchain_root=/path/to/toolchain/root --skip_tests
```

### Documentation Updates
Relevant sections of the documentation will be updated to reflect the
newly supported RISC-V 64-bit cross-compilation feature.
https://github.com/microsoft/onnxruntime/pull/19239

---------

Signed-off-by: Phoebe Chen <phoebe.chen@sifive.com>