[libspirv] Delete clc_* files in generic math and re-use clc (#19165)

llvm-diff shows a lot of changes, including
* __nv_ldexp and __nvvm_reflect_ocl calls are newly added
__spirv_ocl_remquo/tanpi in libspirv-nvptx64--nvidiacl.bc.
* __ocml_ldexp_f64 is replaced with llvm.ldexp.f64.i32 in
__spirv_ocl_remquo in libspirv-amdgcn--amdhsa.bc.
The changes look reasonable since some functions are replaced with clc
implementations.

Author: wenju-he

libclc/libspirv/lib/generic/SOURCES

@@ -65,13 +65,6 @@ math/atanh.cl
 math/atanpi.cl
 math/cbrt.cl
 math/ceil.cl
-math/clc_exp10.cl
-math/clc_fmod.cl
-math/clc_remainder.cl
-math/clc_remquo.cl
-math/clc_rootn.cl
-math/clc_tan.cl
-math/clc_tanpi.cl
 math/copysign.cl
 math/cos.cl
 math/cosh.cl
@@ -82,7 +75,6 @@ math/erfc.cl
 math/exp.cl
 math/exp10.cl
 math/exp2.cl
-math/exp_helper.cl
 math/expm1.cl
 math/fabs.cl
 math/fdim.cl