[dv] Lock tool_srcs_dir before copying sources

- This will be needed soon when we start having multiple builds for the
same DUT.

Signed-off-by: Srikrishna Iyer <sriyer@google.com>
diff --git a/hw/dv/data/sim.mk b/hw/dv/data/sim.mk
index a33ff84..72d111a 100644
--- a/hw/dv/data/sim.mk
+++ b/hw/dv/data/sim.mk
@@ -4,6 +4,7 @@
 
 .DEFAULT_GOAL := all
 
+LOCK_TOOL_SRCS_DIR ?= flock --timeout 3600 ${tool_srcs_dir} --command
 LOCK_SW_BUILD ?= flock --timeout 3600 ${sw_build_dir} --command
 
 all: build run
@@ -16,7 +17,7 @@
 prep_tool_srcs:
 	@echo "[make]: prep_tool_srcs"
 	mkdir -p ${tool_srcs_dir}
-	cp -Ru ${tool_srcs} ${tool_srcs_dir}/.
+	${LOCK_TOOL_SRCS_DIR} "cp -Ru ${tool_srcs} ${tool_srcs_dir}/."
 
 pre_compile:
 	@echo "[make]: pre_compile"