per-config build output using VPATH

based on https://make.mad-scientist.net/papers/multi-architecture-builds/

example/Makefile

@@ -24,7 +24,7 @@ ifeq (,$(filter _out_%,$(notdir $(CURDIR))))
 else
 #----- End Boilerplate
 
-VPATH	  = $(SRCDIR)
+VPATH = $(SRCDIR)
 
 CARGO ?= cargo
 STRIP ?= strip
@@ -94,7 +94,6 @@ ifeq ($(LTO), 1)
 	CFLAGS += -flto
 endif
 
-
 # TODO: wildcard does not work with VPATH
 _c_src := src/announce.c src/brightness_tester.c src/header_logger.c \
 	src/moving_line.c src/random_stuff.c src/wiping_clear.c
@@ -121,16 +120,5 @@ build-rust: FORCE
 
 FORCE: ;
 
-help:
-	@echo "You have the choice of the following parameters:"
-	@echo ""
-	@echo "Variable | Description                       | Default   | Values"
-	@echo "---------+-----------------------------------+-----------+---------------------------"
-	@echo "CARGO    | which cargo binary to use         | 'cargo'   | 'rustup run nightly cargo'"
-	@echo "CC       | which C compiler to use           | 'gcc'     | 'musl-gcc'"
-	@echo "STRIP    | which strip command to use        | 'strip'   | -"
-	@echo "MUSL     | if set, use musl instead of glibc | unset     | '1'"
-	@echo "PROFILE  | Compilation profile               | 'release' | 'debug' or 'size-optimized'"
-
 #----- Begin Boilerplate
 endif

example/target.mk

@@ -33,6 +33,20 @@ Makefile : ;
 # and the source directory containing only source files, `clean' is as trivial
 # as removing the target directories!
 #
-.PHONY: clean
+.PHONY: clean clean-all
 clean:
 	rm -rf $(OBJDIR)
+clean-all:
+	rm -rf _out_*
+
+help:
+	@echo "You have the choice of the following parameters:"
+	@echo ""
+	@echo "Variable | Description          | Default   | Values"
+	@echo "---------+----------------------+-----------+---------------------------"
+	@echo "LIBC     | libc to link against | 'gnu'     | 'gnu' or 'musl'"
+	@echo "PROFILE  | Optimization profile | 'release' | 'debug' or 'size-optimized'"
+	@echo "LINK     |                      | 'dynamic' | 'dynamic' or 'static'"
+	@echo "CARGO    | cargo binary to use  | 'cargo'   | 'rustup run nightly cargo'"
+	@echo "CC       | C compiler to use    | 'gcc'     | 'musl-gcc'"
+	@echo "STRIP    | strip command to use | 'strip'   | -"