makefile: reduce number of shell invocations

While debugging a problem, I discovered that I can list all
the shell commands run in make using the command below.

Modified Makefile so that klayout version is resolved once
instead of many times.

make ".SHELLFLAGS=--verbose -o pipefail -c" open_synth

Signed-off-by: Øyvind Harboe <[email protected]>

Author: oharboe

flow/Makefile

@@ -312,7 +312,9 @@ KLAYOUT_BIN_FROM_DIR = $(KLAYOUT_DIR)/klayout
 ifeq ($(wildcard $(KLAYOUT_BIN_FROM_DIR)), $(KLAYOUT_BIN_FROM_DIR))
 KLAYOUT_CMD ?= sh -c 'LD_LIBRARY_PATH=$(dir $(KLAYOUT_BIN_FROM_DIR)) $$0 "$$@"' $(KLAYOUT_BIN_FROM_DIR)
 else
-KLAYOUT_CMD ?= $(shell command -v klayout)
+ifeq ($(KLAYOUT_CMD),)
+KLAYOUT_CMD := $(shell command -v klayout)
+endif
 endif
 KLAYOUT_FOUND            = $(if $(KLAYOUT_CMD),,$(error KLayout not found in PATH))
 
@@ -404,7 +406,7 @@ do-klayout_tech:
 	cp $(TECH_LEF) $(OBJECTS_DIR)/klayout_tech.lef
 
 KLAYOUT_ENV_VAR_IN_PATH_VERSION = 0.28.11
-KLAYOUT_VERSION = $(shell $(KLAYOUT_CMD) -v 2>/dev/null | grep 'KLayout' | cut -d ' ' -f2)
+KLAYOUT_VERSION := $(shell $(KLAYOUT_CMD) -v 2>/dev/null | grep 'KLayout' | cut -d ' ' -f2)
 
 KLAYOUT_ENV_VAR_IN_PATH = $(shell \
 	if [ -z "$(KLAYOUT_VERSION)" ]; then \