[cmake] Normalize TARGET_SUBDIR paths (#138524)

Some code paths normalize ".." and thus don't create the directory. But some execute in a
shell thus requiring the directory to exist to be able to take the parent directory.

This patch normalizes all the `TARGET_SUBDIR` variables to avoid this issue.

libunwind/CMakeLists.txt

@@ -145,6 +145,7 @@ if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   if(LIBUNWIND_LIBDIR_SUBDIR)
     string(APPEND LIBUNWIND_TARGET_SUBDIR /${LIBUNWIND_LIBDIR_SUBDIR})
   endif()
+  cmake_path(NORMAL_PATH LIBUNWIND_TARGET_SUBDIR)
   set(LIBUNWIND_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LIBUNWIND_TARGET_SUBDIR})
   set(LIBUNWIND_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LIBUNWIND_TARGET_SUBDIR} CACHE STRING
       "Path where built libunwind libraries should be installed.")