libclc: Allow building with only required LLVM libs and with custom CLC/LLAsm flags

[callumfare]

Summary

• Only call llvm-config --system-libs with the required libraries so libclc doesn't depend on all LLVM components being built.
• Handle CMAKE_CLC_FLAGS and CMAKE_LLAsm_FLAGS correctly so users can pass custom flags

This contribution is being made by Codeplay on behalf of Samsung.

[rjodinchr]

Everything in this patch has already been merged upstream.
It can be dropped

[kpet]

I can confirm that the flag quoting is present upstream and that the other change does not apply any more. Closing as suggested by @rjodinchr .

libclc/CMakeLists.txt

 if( ${LLVM_VERSION} VERSION_GREATER "3.9.0" )
   set( LIBCLC_TARGETS_ALL ${LIBCLC_TARGETS_ALL} amdgcn-mesa-mesa3d )
 endif()
 
 if( LIBCLC_TARGETS_TO_BUILD STREQUAL "all" )
   set( LIBCLC_TARGETS_TO_BUILD ${LIBCLC_TARGETS_ALL} )
 endif()
 
-execute_process( COMMAND ${LLVM_CONFIG} "--system-libs"
+execute_process( COMMAND ${LLVM_CONFIG} "--system-libs" "core" "bitreader" "bitwriter"
   OUTPUT_VARIABLE LLVM_SYSTEM_LIBS
   OUTPUT_STRIP_TRAILING_WHITESPACE )
 separate_arguments( LLVM_SYSTEM_LIBS )
 execute_process( COMMAND ${LLVM_CONFIG} "--libs" "core" "bitreader" "bitwriter"
   OUTPUT_VARIABLE LLVM_LIBS
   OUTPUT_STRIP_TRAILING_WHITESPACE )
 separate_arguments( LLVM_LIBS )
 execute_process( COMMAND ${LLVM_CONFIG} "--libdir"

 string( REPLACE "." ";" LLVM_VERSION_LIST ${LLVM_VERSION} )
 list( GET LLVM_VERSION_LIST 0 LLVM_MAJOR )
 list( GET LLVM_VERSION_LIST 1 LLVM_MINOR )
 set( LLVM_VERSION_DEFINE "-DHAVE_LLVM=0x${LLVM_MAJOR}0${LLVM_MINOR}" )
 
 
 # LLVM 13 enables standard includes by default
 if( ${LLVM_VERSION} VERSION_GREATER "12.99.99" )
-        set( CMAKE_LLAsm_FLAGS ${CMAKE_LLAsm_FLAGS} -cl-no-stdinc )
-        set( CMAKE_CLC_FLAGS ${CMAKE_CLC_FLAGS} -cl-no-stdinc )
+        set( CMAKE_LLAsm_FLAGS "${CMAKE_LLAsm_FLAGS} -cl-no-stdinc" )
+        set( CMAKE_CLC_FLAGS "${CMAKE_CLC_FLAGS} -cl-no-stdinc" )
 endif()
 
 enable_language( CLC LLAsm )
 
 # This needs to be set before any target that needs it
 link_directories( ${LLVM_LIBDIR} )
 
 # Setup prepare_builtins tools