Fix when LLVM_USE_INTEL_JITEVENTS and LLVM_USE_OPROFILE not set, llvm-build not gen LibraryDependencies.inc

[fcharlie]

Summary

If LLVM_USE_INTEL_JITEVENTS and LLVM_USE_OPROFILE not set, "${LLVMOPTIONALCOMPONENTS}" is empty, but --enable-optional-components need arg, Cause --write-library-table to be skipped parsed.

My CMake version: 3.11.2

execute_process(
  COMMAND ${PYTHON_EXECUTABLE} -B ${LLVMBUILDTOOL}
            --native-target "${LLVM_NATIVE_ARCH}"
            --enable-targets "${LLVM_TARGETS_TO_BUILD}"
            --enable-optional-components "${LLVMOPTIONALCOMPONENTS}"
            --write-library-table ${LLVMCONFIGLIBRARYDEPENDENCIESINC}
            --write-cmake-fragment ${LLVMBUILDCMAKEFRAG}
            OUTPUT_VARIABLE LLVMBUILDOUTPUT
            ERROR_VARIABLE LLVMBUILDERRORS
            OUTPUT_STRIP_TRAILING_WHITESPACE
            ERROR_STRIP_TRAILING_WHITESPACE
  RESULT_VARIABLE LLVMBUILDRESULT)

[rnk]

lgtm

[fcharlie]

@rnk Please commit this, Thanks

llvm/trunk/CMakeLists.txt

 
 set(LLVMBUILDTOOL "${LLVM_MAIN_SRC_DIR}/utils/llvm-build/llvm-build")
 set(LLVMCONFIGLIBRARYDEPENDENCIESINC
   "${LLVM_BINARY_DIR}/tools/llvm-config/LibraryDependencies.inc")
 set(LLVMBUILDCMAKEFRAG
   "${LLVM_BINARY_DIR}/LLVMBuild.cmake")
 
 # Create the list of optional components that are enabled
+set(LLVM_USE_INTEL_JITEVENTS " ")
 if (LLVM_USE_INTEL_JITEVENTS)
   set(LLVMOPTIONALCOMPONENTS IntelJITEvents)
 endif (LLVM_USE_INTEL_JITEVENTS)
 if (LLVM_USE_OPROFILE)
   set(LLVMOPTIONALCOMPONENTS ${LLVMOPTIONALCOMPONENTS} OProfileJIT)
 endif (LLVM_USE_OPROFILE)
 
 message(STATUS "Constructing LLVMBuild project information")