[Libomptarget] Add header files as a dependency to CMake target

[jhuber6]

Summary

This patch manually adds the runtime include files to the list of
dependencies when we build the bitcode runtime library. Previously if
only the header was changed we would not recompile the source files.
The solution used here isn't optimal because every source file not has a
dependency on each header file regardless of if it was actually used by
that file.

[ronlieb]

Thx
Much needed!

[tianshilei1992]

LG

openmp/libomptarget/DeviceRTL/CMakeLists.txt

if (DEFINED LIBOMPTARGET_AMDGCN_GFXLIST)
   set(amdgpu_mcpus ${LIBOMPTARGET_AMDGCN_GFXLIST})
 endif()
 
 
 # Activate RTL message dumps if requested by the user.
 set(LIBOMPTARGET_DEVICE_DEBUG FALSE CACHE BOOL
   "Activate DeviceRTL debug messages.")
 
+set(include_files
+  ${include_directory}/Configuration.h
+  ${include_directory}/Debug.h
+  ${include_directory}/Interface.h
+  ${include_directory}/Mapping.h
+  ${include_directory}/State.h
+  ${include_directory}/Synchronization.h
+  ${include_directory}/Types.h
+  ${include_directory}/Utils.h
+)
 
 set(src_files
   ${source_directory}/Configuration.cpp
   ${source_directory}/Debug.cpp
   ${source_directory}/Kernel.cpp
   ${source_directory}/Mapping.cpp
   ${source_directory}/Misc.cpp
   ${source_directory}/Parallelism.cpp
foreach(src ${src_files})
     set(outfile "${outfile}-${target_cpu}.bc")
 
     add_custom_command(OUTPUT ${outfile}
       COMMAND ${CLANG_TOOL}
       ${bc_flags}
       -Xclang -target-cpu -Xclang ${target_cpu}
       ${target_bc_flags}
       ${infile} -o ${outfile}
-      DEPENDS ${infile}
+      DEPENDS ${infile} ${include_files}
       IMPLICIT_DEPENDS CXX ${infile}
       COMMENT "Building LLVM bitcode ${outfile}"
       VERBATIM
     )
     if("${CLANG_TOOL}" STREQUAL "$<TARGET_FILE:clang>")
       # Add a file-level dependency to ensure that clang is up-to-date.
       # By default, add_custom_command only builds clang if the
       # executable is missing.