u64 with `trailing_zeros` returns incorrect values

Expected Behaviour

We expect the trailing_zeros() function on u64 values to match the behavior of Rust's standard library implementation, returning the count of trailing zero bits.

For example:

• 0x0000000000000001_u64.trailing_zeros() should return 0
• 0x0000000100000000_u64.trailing_zeros() should return 32
• 0x8000000000000000_u64.trailing_zeros() should return 63

Example & Steps To Reproduce

• 0x0000000000000001 Expected: 0, Result: 32
• 0x0000000100000000 Expected: 32, Result: 0
• 0x8000000000000000 Expected: 63, Result: 31

Run a shader that calculates trailing zeros on a u64. I am creating a pull request that contains test to validate the function and a fix for this issue.

#![no_std]
use spirv_std::spirv;

#[spirv(compute(threads(1)))]
pub fn main_cs(
    #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] output: &mut [u32],
) {
    // Expected: 0, Actual: 32
    output[0] = 0x0000000000000001_u64.trailing_zeros();
    
    // Expected: 32, Actual: 0  
    output[1] = 0x0000000100000000_u64.trailing_zeros();
}

Start by tracing the u64 trailing_zeros() entry point used when compiling the shader, comparing its behavior with Rust's standard library implementation. Run the shader reproduction with the three listed u64 values and add or use tests covering results 0, 32, and 63. Done means all examples return the expected count of trailing zero bits.