arm64: vdso32: drop -no-integrated-as flag

Clang can assemble these files just fine; this is a relic from the top
level Makefile conditionally adding this. We no longer need --prefix,
--gcc-toolchain, or -Qunused-arguments flags either with this change, so
remove those too.

To test building:
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
  CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 LLVM_IAS=1 \
  defconfig arch/arm64/kernel/vdso32/

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210420174427.230228-1-ndesaulniers@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/vdso32/Makefile

@@ -10,15 +10,7 @@ include $(srctree)/lib/vdso/Makefile
 
 # Same as cc-*option, but using CC_COMPAT instead of CC
 ifeq ($(CONFIG_CC_IS_CLANG), y)
-COMPAT_GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE_COMPAT)elfedit))
-COMPAT_GCC_TOOLCHAIN := $(realpath $(COMPAT_GCC_TOOLCHAIN_DIR)/..)
-
 CC_COMPAT_CLANG_FLAGS := --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
-CC_COMPAT_CLANG_FLAGS += --prefix=$(COMPAT_GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE_COMPAT))
-CC_COMPAT_CLANG_FLAGS += -no-integrated-as -Qunused-arguments
-ifneq ($(COMPAT_GCC_TOOLCHAIN),)
-CC_COMPAT_CLANG_FLAGS += --gcc-toolchain=$(COMPAT_GCC_TOOLCHAIN)
-endif
 
 CC_COMPAT ?= $(CC)
 CC_COMPAT += $(CC_COMPAT_CLANG_FLAGS)