If the experimental feature Wasm build enabled with multi thread
compiling, the COPYFILE (cp) maybe raise the error below:
```
cp: cannot create regular file 'math.h': file exists
```
This error cause by that the wasi-sdk don't provide the math.h for
non-wasi envrioment, for this case, provide a math.h for it instead of copy
file each time is better.
Signed-off-by: Huang Qi <huangqi3@xiaomi.com>