XCVsimd builtin optimisation enhancement

Created by: zhixiao-zhang

added (compile and pass the related testing in gcc.target/riscv/):

• simd alu
• simd bit manipulation
• simd dot product
• simd shuffle and pack
• simd comparison
• simd complex

tested with emulator

• simd alu
• simd bit manipulation
• simd dot product
• simd shuffle and pack
• simd comparison
• simd complex

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