Expands make variables using macrostep-expand interface from macrostep.
Variables are retrieved from make's internal database using make -prns. They
are updated when the buffer's file's modication time changes.
The following functions are defined for the macrostep interface:
+ macrostep-sexp-bounds-function
+ macrostep-sexp-at-point-function
+ macrostep-environment-at-point-function
+ macrostep-expand-1-function
+ macrostep-print-function
Require macrostep and macrostep-make.
Bind macrostep-expand to a key, eg (kbd C-c e).
Then, in makefiles, C-c e interactively expands variables at point.
