platform.mk: Define empty, space, comma

The PYTHONPATH export in py-path.mk is built by substituting the spaces of
the space-separated JW_PKG_PYTHON_PATH list with colons, using "space" from
defs.mk. Which may not be included if somebody wants to include a bare
py-defs.mk, so define it in platform.mk. Not happening in jw-pkg, but nice
to have.

Signed-off-by: Jan Lindemann <jan@janware.com>

make/defs.mk

@@ -7,10 +7,6 @@ JW_PKG_DEF_MK_INCLUDED       = true
 
 MAKEFLAGS                   += -r
 
-empty                       :=
-space                       := $(empty) $(empty)
-comma                       := ,
-
 include $(JWBDIR)/make/projects.mk
 
 # ----- Executables

make/platform.mk

@@ -3,6 +3,10 @@
 ifndef PLATFORM_MK_INCLUDED
 PLATFORM_MK_INCLUDED         = true
 
+empty                       :=
+space                       := $(empty) $(empty)
+comma                       := ,
+
 CACHE_PROJECT_MK            ?= $(TOPDIR)/.cache-project.mk
 CACHE_PROJECTS_MK           := $(JWBDIR)/.cache-projects.mk
 JW_PKG_NO_CACHE             ?= false