qemu_armv8a: fix build with CFG_USER_TA_TARGETS=ta_arm32

The proper way to build in-tree TAs in 64-bit mode by default is to set
supported-ta-targets to "ta_arm64 ta_arm32". Indeed, the default target
is always defined as the first entry in supported-ta-targets, as
documented in mk/config.mk.

Fixes the following build error:

 $ make CFG_USER_TA_TARGETS=ta_arm32 PLATFORM=vexpress-qemu_armv8a
 bash: -W: invalid option
 ...

default-user-ta-target is not to be used by the platform configuration
files. It is meant to be set by the main Makefile. For this reason,
replace the conditional assignment (?=) with $(call force, ...) in order
to catch inconsistencies in a more friendly way.

Fixes: 07031b2 ("qemu_armv8a: set default-user-ta-target ?= ta_arm64")
Signed-off-by: Jerome Forissier <[email protected]>
Acked-by: Etienne Carriere <[email protected]>
Acked-by: Jens Wiklander <[email protected]>

Makefile

@@ -79,7 +79,7 @@ include core/core.mk
 
 # Platform/arch config is supposed to assign the targets
 ta-targets ?= invalid
-default-user-ta-target ?= $(firstword $(ta-targets))
+$(call force,default-user-ta-target,$(firstword $(ta-targets)))
 
 ifeq ($(CFG_WITH_USER_TA),y)
 include ldelf/ldelf.mk

core/arch/arm/plat-vexpress/conf.mk

@@ -23,7 +23,7 @@ endif #juno
 ifeq ($(PLATFORM_FLAVOR),qemu_armv8a)
 include core/arch/arm/cpu/cortex-armv8-0.mk
 CFG_ARM64_core ?= y
-default-user-ta-target ?= ta_arm64
+supported-ta-targets ?= ta_arm64 ta_arm32
 endif