message: Fix race condition in parallel Makefile
  Some recipes require the headers, but they don't explicitly say
  so. Parallel make (-j`nproc`) might start compiling the libs when the
  headers aren't done yet.
diff: @@ -27,11 +27,12 @@ SRC=\
  src/* \
  src/*/* \
  src/*/*/* \
  - src/*/*/*/*
  + src/*/*/*/* \
  + headers # Used by compiler-builtins
  .PHONY: all clean fmt headers install install-headers libs test
  -all: | headers libs
  +all: headers libs
  clean:
  $(CARGO) clean
  @@ -179,7 +180,7 @@ $(BUILD)/include: $(SRC)
  mv $@.partial $@
  touch $@
  -$(BUILD)/openlibm: openlibm
  +$(BUILD)/openlibm: openlibm headers
  rm -rf $@ $@.partial
  mkdir -p $(BUILD)
  cp -r $< $@.partial
  @@ -189,7 +190,7 @@ $(BUILD)/openlibm: openlibm
  $(BUILD)/openlibm/libopenlibm.a: $(BUILD)/openlibm $(BUILD)/include
  $(MAKE) CC=$(CC) CPPFLAGS="-fno-stack-protector -I$(shell pwd)/include -I $(shell pwd)/$(BUILD)/include" -C $< libopenlibm.a
  -$(BUILD)/pthreads-emb: pthreads-emb
  +$(BUILD)/pthreads-emb: pthreads-emb headers
  rm -rf $@ $@.partial
  mkdir -p $(BUILD)
  cp -r $< $@.partial
  