message: Prepare for cross compiled openlibm
diff: +TARGET?=
  +
  +BUILD=target/debug
  +ifneq ($(TARGET),)
  + BUILD=target/$(TARGET)/debug
  + CARGOFLAGS+="--target=$(TARGET)"
  + CC=$(TARGET)-gcc
  +endif
  +
  .PHONY: all clean fmt test
  -all: openlibm/libopenlibm.a target/debug/libc.a target/debug/libcrt0.a
  - cargo build
  +all: $(BUILD)/libc.a $(BUILD)/libcrt0.a $(BUILD)/openlibm/libopenlibm.a
  clean:
  cargo clean
  - make -C openlibm clean
  make -C tests clean
  fmt:
  ./fmt.sh
  -test: openlibm/libopenlibm.a
  +test: all
  make -C tests run
  -target/debug/libc.a:
  - cargo build
  +$(BUILD)/libc.a:
  + cargo build $(CARGOFLAGS)
  +
  +$(BUILD)/libcrt0.a:
  + cargo build --manifest-path src/crt0/Cargo.toml $(CARGOFLAGS)
  -target/debug/libcrt0.a:
  - cargo build --manifest-path src/crt0/Cargo.toml
  +$(BUILD)/openlibm: openlibm
  + rm -rf $@ $@.partial
  + cp -r $< $@.partial
  + mv $@.partial $@
  -openlibm/libopenlibm.a:
  - CFLAGS=-fno-stack-protector make -C openlibm libopenlibm.a
  +$(BUILD)/openlibm/libopenlibm.a: $(BUILD)/openlibm
  + CC=$(CC) CFLAGS=-fno-stack-protector make -C $< libopenlibm.a
  