Search for tablegen only in LLVM prebuild mode (#295)

Author: intel-kzhavoro

CMakeLists.txt

@@ -143,9 +143,9 @@ endif(NOT USE_PREBUILT_LLVM)
 #
 set (COMPILE_OPTIONS_TD  opencl_clang_options.td)
 set (COMPILE_OPTIONS_INC opencl_clang_options.inc)
-find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR})
 set(LLVM_TARGET_DEFINITIONS ${COMPILE_OPTIONS_TD})
 if(USE_PREBUILT_LLVM)
+  find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR})
   set(TABLEGEN_ADDITIONAL -I ${LLVM_INCLUDE_DIRS})
 else(USE_PREBUILT_LLVM)
   set(TABLEGEN_ADDITIONAL "")