Revert "kbuild: Remove support for Clang's ThinLTO caching"

This reverts commit 8dd62e3.

Signed-off-by: Yahya Wessam <yahyawessam2002@gmail.com>

Author: pascua28

Makefile

@@ -958,7 +958,7 @@ endif
 ifdef CONFIG_LTO_CLANG
 ifdef CONFIG_THINLTO
 lto-clang-flags	:= -flto=thin -fsplit-lto-unit $(call cc-option,-funified-lto)
-LDFLAGS		+= --thinlto-jobs=$(nproc --all)
+LDFLAGS		+= --thinlto-cache-dir=.thinlto-cache --thinlto-jobs=$(nproc --all)
 
 # LLVM tunings
 KBUILD_LDFLAGS += -mllvm -inline-threshold=500