ARM: don't use --gc-sections with LTO when using private libgcc

When using LTO, we can throw away the --gc-sections flag, but only if
using private libgcc.

When using system's libgcc, --gc-sections is still needed, otherwise
linking will fail due to undefined references to libc's symbols.
Signed-off-by: NMarek Behún <marek.behun@nic.cz>
Reviewed-by: NSimon Glass <sjg@chromium.org>

arch/arm/config.mk

@@ -15,7 +15,9 @@ CFLAGS_NON_EFI := -fno-pic -ffixed-r9 -ffunction-sections -fdata-sections \
 		  -fstack-protector-strong
 CFLAGS_EFI := -fpic -fshort-wchar
 
+ifneq ($(CONFIG_LTO)$(CONFIG_USE_PRIVATE_LIBGCC),yy)
 LDFLAGS_FINAL += --gc-sections
+endif
 
 ifndef CONFIG_LTO
 PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections