vboot_ref/Makefile: Expose symbols irregardless of USE_FLASHROM

subproccess helpers are only used by flashrom.c at the moment. However we
temporarily need the symbols to bridge the gap with cbfstools/elogtool in
upstream coreboot. Furthmore, there are new additional use-cases for
subproccess in other parts of vboot_reference unrelated to flashrom
directly.

BUG=b:231152447
BRANCH=none
TEST=builds

Change-Id: Id8008eefd46efa329adf76323800bb7646bf922c
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3697856
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Julius Werner <jwerner@chromium.org>
Auto-Submit: Edward O'Callaghan <quasisec@chromium.org>
diff --git a/Makefile b/Makefile
index 5f5b706..abbb343 100644
--- a/Makefile
+++ b/Makefile
@@ -447,10 +447,10 @@
 FLASHROM_LIBS := $(shell ${PKG_CONFIG} --libs flashrom)
 COMMONLIB_SRCS = \
 	host/lib/flashrom.c \
-	host/lib/flashrom_drv.c \
-	host/lib/subprocess.c
+	host/lib/flashrom_drv.c
 CFLAGS += -DUSE_FLASHROM
 endif
+COMMONLIB_SRCS += host/lib/subprocess.c
 
 # Intermediate library for the vboot_reference utilities to link against.
 UTILLIB = ${BUILD}/libvboot_util.a