OpenMP/cmake: Use DEPFILE instead of IMPLICIT_DEPENDS

IMPLICIT_DEPENDS doesn't actually work with ninja and this does.

GitOrigin-RevId: a2f5bcc766fb77118630e13c91c3f3f2fd43420a

libomptarget/DeviceRTL/CMakeLists.txt

diff --git a/libomptarget/DeviceRTL/CMakeLists.txt b/libomptarget/DeviceRTL/CMakeLists.txt
index 7540a8c..8068904 100644
--- a/libomptarget/DeviceRTL/CMakeLists.txt
+++ b/libomptarget/DeviceRTL/CMakeLists.txt
@@ -138,15 +138,17 @@
     get_filename_component(infile ${src} ABSOLUTE)
     get_filename_component(outfile ${src} NAME)
     set(outfile "${outfile}-${target_cpu}.bc")
+    set(depfile "${outfile}.d")
 
     add_custom_command(OUTPUT ${outfile}
       COMMAND ${CLANG_TOOL}
       ${bc_flags}
       --offload-arch=${target_cpu}
       ${target_bc_flags}
+      -MD -MF ${depfile}
       ${infile} -o ${outfile}
-      DEPENDS ${infile} ${include_files}
-      IMPLICIT_DEPENDS CXX ${infile}
+      DEPENDS ${infile}
+      DEPFILE ${depfile}
       COMMENT "Building LLVM bitcode ${outfile}"
       VERBATIM
     )