arm64: build with baremetal linker target instead of Linux when available

Not all toolchains have the baremetal elf targets, RedHat/Fedora ones
in particular. So, probe for whether it's available and use the previous
(linux) targets if it isn't.
Reported-by: Laura Abbott <labbott@redhat.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/Makefile

@@ -60,15 +60,16 @@ ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__
 AS		+= -EB
-LD		+= -EB
-LDFLAGS		+= -maarch64linuxb
+# Prefer the baremetal ELF build target, but not all toolchains include
+# it so fall back to the standard linux version if needed.
+LDFLAGS		+= -EB $(call ld-option, -maarch64elfb, -maarch64linuxb)
 UTS_MACHINE	:= aarch64_be
 else
 KBUILD_CPPFLAGS	+= -mlittle-endian
 CHECKFLAGS	+= -D__AARCH64EL__
 AS		+= -EL
-LD		+= -EL
-LDFLAGS		+= -maarch64linux
+# Same as above, prefer ELF but fall back to linux target if needed.
+LDFLAGS		+= -EL $(call ld-option, -maarch64elf, -maarch64linux)
 UTS_MACHINE	:= aarch64
 endif
 

scripts/Kbuild.include

@@ -163,8 +163,8 @@ cc-ldoption = $(call try-run,\
 	$(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
 
 # ld-option
-# Usage: LDFLAGS += $(call ld-option, -X)
-ld-option = $(call try-run, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2))
+# Usage: LDFLAGS += $(call ld-option, -X, -Y)
+ld-option = $(call try-run, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2),$(3))
 
 # ar-option
 # Usage: KBUILD_ARFLAGS := $(call ar-option,D)