[libspirv] Avoid macro redefinition (intel#18670)

The macro __CLC_FUNCTION is special and is used in CLC headers. Defining
it here in an implementation file - nextafter.cl - for another purpose
then including half_nextafter.inc which pulls in the SPIR-V headers
results in a macro redefinition, which is warned about.

Sicne the name isn't important and is local to this one file, this
commit just changes the macro definition to fix the issue.

Author: frasercrmck

libclc/libspirv/lib/ptx-nvidiacl/math/nextafter.cl

@@ -11,20 +11,21 @@
 #include <clc/utils.h>
 #include <libspirv/spirv.h>
 
-#define __CLC_FUNCTION __spirv_ocl_nextafter
+#define __SPIRV_FUNCTION __spirv_ocl_nextafter
 #define __CLC_BUILTIN __nv_nextafter
 #define __CLC_BUILTIN_F __CLC_XCONCAT(__CLC_BUILTIN, f)
 #define __CLC_BUILTIN_D __CLC_BUILTIN
 
-_CLC_DEFINE_BINARY_BUILTIN(float, __CLC_FUNCTION, __CLC_BUILTIN_F, float, float)
+_CLC_DEFINE_BINARY_BUILTIN(float, __SPIRV_FUNCTION, __CLC_BUILTIN_F, float,
+                           float)
 
 #ifndef __FLOAT_ONLY
 
 #ifdef cl_khr_fp64
 
 #pragma OPENCL EXTENSION cl_khr_fp64 : enable
 
-_CLC_DEFINE_BINARY_BUILTIN(double, __CLC_FUNCTION, __CLC_BUILTIN_D, double,
+_CLC_DEFINE_BINARY_BUILTIN(double, __SPIRV_FUNCTION, __CLC_BUILTIN_D, double,
                            double)
 
 #endif