Update makefile

Makefile

@@ -40,6 +40,12 @@ CLEAN_FS?=build \
 # Default: include.mk
 INCLUDE_MAKEFILE?=include.mk
 
+# Optional additional directories to be added to PATH in format
+# `/path/to/dir/:/path/to/other/dir`. Gets inserted first, thus gets searched
+# first.
+# No default value.
+EXTRA_PATH?=
+
 ## js.npm
 
 # Value for `--prefix` option.
@@ -159,6 +165,8 @@ DIRTY_TARGETS?=
 CLEAN_TARGETS?=
 PURGE_TARGETS?=
 
+export PATH:=$(if $(EXTRA_PATH),"$(EXTRA_PATH):","")$(PATH)
+
 # Defensive settings for make: https://tech.davis-hansson.com/p/make/
 SHELL:=bash
 .ONESHELL:
@@ -183,7 +191,7 @@ $(SENTINEL):
 # npm
 ##############################################################################
 
-export PATH:=$(shell pwd)/$(NPM_PREFIX)/node_modules/.bin/:$(PATH)
+export PATH:=$(shell pwd)/$(NPM_PREFIX)/node_modules/.bin:$(PATH)
 
 # case `system.dependencies` domain is included
 SYSTEM_DEPENDENCIES+=npm
@@ -301,7 +309,7 @@ endif
 
 # determine the executable path
 ifeq ("$(VENV_ENABLED)", "true")
-export PATH:=$(shell pwd)/$(VENV_FOLDER)/bin/:$(PATH)
+export PATH:=$(shell pwd)/$(VENV_FOLDER)/bin:$(PATH)
 export VIRTUAL_ENV=$(VENV_FOLDER)
 MXENV_PYTHON=python
 else