libutils: embed AEABI personality routines upon CFG_UNWIND

Fix a TA build issue found when CFG_UNWIND=n. This issue produces a
build error trace like the below:

.../toolchains/aarch32/bin/arm-linux-gnueabihf-ld.bfd: .../toolchains/aarch32/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/libgcc_eh.a(unwind-arm.o): in function `__aeabi_unwind_cpp_pr0':
/tmp/dgboter/bbs/rhev-vm8--rhe6x86_64/buildbot/rhe6x86_64--arm-linux-gnueabihf/build/src/gcc/libgcc/config/arm/unwind-arm.c:494: multiple definition of `__aeabi_unwind_cpp_pr0'; .../optee_os/out/arm/export-ta_arm32/lib/libutils.a(aeabi_unwind.o): .../optee_os/lib/libutils/ext/arch/arm/aeabi_unwind.c:9: first defined here
.../optee_os/out/arm/export-ta_arm32/mk/link.mk:109: recipe for target 'out/5b9e0e40-2636-11e1-ad9e-0002a5d5c51b.elf' failed

I don't understand why toolchain support for __aeabi_unwind_cpp_pr0()
conflicts with the libutils implementation only when CFG_UNWIND=n. Yet
the current change works around the issue.

Fixes: OP-TEE/optee_test#440
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Jerome Forissier <jerome@forissier.org>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>

lib/libutils/ext/arch/arm/sub.mk

@@ -1,4 +1,6 @@
+ifeq ($(CFG_UNWIND),y)
 srcs-$(CFG_ARM32_$(sm)) += aeabi_unwind.c
+endif
 srcs-$(CFG_ARM32_$(sm)) += atomic_a32.S
 srcs-$(CFG_ARM64_$(sm)) += atomic_a64.S
 ifneq ($(sm),ldelf) # TA, core