makefile: add pwd non-source control settings.mk file

this allows setting up settings that are not supposed to
be persisted to source control.

If you add DESIGN_CONFIG=.../config.mk, you can exclude the
DESIGN_CONFIG=... from the make command line.

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

Author: oharboe

flow/.gitignore

@@ -0,0 +1 @@
+settings.mk

flow/Makefile

@@ -1,3 +1,7 @@
+# settings.mk is not under source control. Put variables into this
+# file to avoid having to adding the to the make command line.
+-include settings.mk
+
 # ==============================================================================
 # Uncomment or add the design to run
 # ==============================================================================