With this PR, if we have customized implementation for scalar or vector
length = 2, we don't need to write new macros, e.g.
https://github.com/intel/llvm/blob/fb18321705f6/libclc/clc/include/clc/clcmacro.h#L15
Undef __HALF_ONLY, __FLOAT_ONLY and __DOUBLE_ONLY at the end of
clc/include/clc/math/gentype.inc
llvm-diff shows no change to nvptx64--nvidiacl.bc and amdgcn--amdhsa.bc