[libclc]: clspv: add a dummy implememtation for mul_hi (llvm#134094)

clspv uses a better implementation that is not using a bigger side when
not available.
Add a dummy implementation for mul_hi to avoid to override the
implementation of clspv with the one in libclc.

Author: rjodinchr

libclc/clc/lib/clspv/SOURCES

@@ -1 +1,2 @@
 math/clc_sw_fma.cl
+integer/clc_mul_hi.cl

libclc/clc/lib/clspv/integer/clc_mul_hi.cl

@@ -0,0 +1,5 @@
+/*
+Opt-out of libclc mul_hi implementation for clspv.
+clspv has an internal implementation that does not required using a bigger data size.
+That implementation is based on OpMulExtended which is SPIR-V specific, thus it cannot be written in OpenCL-C.
+*/