[LoongArch][Clang] Make the parameters and return value of {x,}vxor.v builti ns `unsigned char` vectors (#114513)
The lsxintrin.h and and lasxintrin.h headers uses `unsigned char`
vectors instead of `signed char` vectors. GCC also uses `unsigned char`
for them, so align their definition with the headers and GCC.
Fixes #110834.
Depends on #114512.