linking: add and use LDFLAGS_common

Add an LDFLAGS_common variable and use that for each stage
during linking within all the architectures. All the architectures
support gc-sections, and as such they should be linking in the
same way.

BUG=chrome-os-partner:44827
BRANCH=None
TEST=Built rambi and analyzed the relocatable ramstage.

Change-Id: I41fbded54055455889b297b9e8738db4dda0aad0
Signed-off-by: Aaron Durbin <adubin@chromium.org>
Reviewed-on: http://review.coreboot.org/11522
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>

Makefile.inc

@@ -278,6 +278,8 @@ CFLAGS_common += -Wstrict-aliasing -Wshadow
 CFLAGS_common += -fno-common -ffreestanding -fno-builtin -fomit-frame-pointer
 CFLAGS_common += -ffunction-sections -fdata-sections
 
+LDFLAGS_common := --gc-sections -nostdlib -nostartfiles -static --emit-relocs
+
 ifeq ($(CONFIG_COMPILER_GCC),y)
 # cf. commit f69a99db (coreboot: x86: enable gc-sections)
 CFLAGS_common += -Wno-unused-but-set-variable