variables: break out variables.mk file

The idea is to separate the ORFS variable support and make
variables and ORFS agnostic to build systems, even if
make is used to evaluate variables.

ORFS contains an implementation of a flow using make,
bazel-orfs implements a flow using Bazel.

Sometimes make is preferable, keep things simple, but for more advanced
flows, Bazel provides more flexibility at the cost of increased complexity.

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

Author: oharboe

flow/Makefile

@@ -85,11 +85,6 @@
 # Default design
 DESIGN_CONFIG ?= ./designs/nangate45/gcd/config.mk
 
-# Include design and platform configuration before setting default options
-# in this file. This allows the DESIGN_CONFIG to set different defaults than
-# this file.
-include $(DESIGN_CONFIG)
-export DESIGN_NICKNAME?=$(DESIGN_NAME)
 # default value "base" is duplicated from variables.yaml because we need it
 # earlier in the flow for BLOCKS. BLOCKS is a feature specific to Makefile
 # that will not be ported to bazel-orfs.
@@ -138,6 +133,7 @@ MAKEFLAGS += --no-builtin-rules
 SHELL          := /usr/bin/env bash
 .SHELLFLAGS    := -o pipefail -c
 
+
 #-------------------------------------------------------------------------------
 # Setup variables to point to root / head of the OpenROAD directory
 # - the following settings allowed user to point OpenROAD binaries to different
@@ -148,6 +144,8 @@ FLOW_HOME := $(abspath $(dir $(firstword $(MAKEFILE_LIST))))
 endif
 export FLOW_HOME
 
+include $(FLOW_HOME)/scripts/variables.mk
+
 #-------------------------------------------------------------------------------
 # Setup variables to point to other location for the following sub directory
 # - designs - default is under current directory

flow/scripts/variables.mk

@@ -0,0 +1,10 @@
+# Sets up ORFS variables using make variable support, relying
+# on makefile features such as defaults, forward references,
+# lazy evaluation, conditional code, include statements,
+# etc.
+
+# Include design and platform configuration before setting default options
+# in this file. This allows the DESIGN_CONFIG to set different defaults than
+# this file.
+include $(DESIGN_CONFIG)
+export DESIGN_NICKNAME?=$(DESIGN_NAME)