When building with CONFIG_EFI and CONFIG_EFI_STUB on ARM, the libstub
Makefile would use -mno-single-pic-base without checking it was
supported by the compiler. As the ARM (32-bit) clang backend does not
support this flag, the build would fail.

This changes the Makefile to check the compiler's support for
-mno-single-pic-base before using it, similar to c1c386681bd7 ("ARM:
8767/1: add support for building ARM kernel with clang").

Cc: Stefan Agner <ste...@agner.ch>
Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Russell King <li...@armlinux.org.uk>
Cc: linux-efi@vger.kernel.org
Cc: linux-arm-ker...@lists.infradead.org
Signed-off-by: Alistair Strachan <astrac...@google.com>
---
 drivers/firmware/efi/libstub/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/Makefile 
b/drivers/firmware/efi/libstub/Makefile
index a34e9290a699..91339d13f2a1 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -13,7 +13,8 @@ cflags-$(CONFIG_X86)          += -m$(BITS) -D__KERNEL__ -O2 \
 
 cflags-$(CONFIG_ARM64)         := $(subst -pg,,$(KBUILD_CFLAGS)) -fpie
 cflags-$(CONFIG_ARM)           := $(subst -pg,,$(KBUILD_CFLAGS)) \
-                                  -fno-builtin -fpic -mno-single-pic-base
+                                  -fno-builtin -fpic \
+                                  $(call cc-option,-mno-single-pic-base)
 
 cflags-$(CONFIG_EFI_ARMSTUB)   += -I$(srctree)/scripts/dtc/libfdt
 
-- 
2.18.0.597.ga71716f1ad-goog

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