Makefile: using FSTAR_EXE and remove FSTAR_HOME

Needs FStarLang/karamel#516

Author: mtzguido

Makefile

@@ -61,7 +61,7 @@ VALE_FLAGS= \
 
 # The usual bug with prims.krml
 dist/Makefile.basic: $(filter-out %prims.krml,$(ALL_KRML_FILES))
-	$(KRML) $(KOPTS) $^ -tmpdir dist -skip-compilation \
+	$(KRML) -fstar $(FSTAR_EXE) $(KOPTS) $^ -tmpdir dist -skip-compilation \
 	  -minimal \
 	  -add-include '"hacl_krmlrenamings.h"' \
 	  -add-include '"krml/internal/target.h"' \

Makefile.include

@@ -1,5 +1,6 @@
 MERKLE_HOME ?= $(realpath .)
 
+FSTAR_EXE ?= $(shell which fstar.exe)
 KRML_HOME ?= $(MERKLE_HOME)/../karamel
 HACL_HOME ?= $(MERKLE_HOME)/../hacl-star
 
@@ -27,7 +28,7 @@ FSTAR_FLAGS=$(FSTAR_CHILL_FLAGS) \
 	--already_cached '*,-MerkleTree,-MerkleTree.*,-Lib.RawBuffer' \
 	--warn_error @241-274 \
 
-FSTAR=$(FSTAR_HOME)/bin/fstar.exe $(FSTAR_FLAGS)
+FSTAR=$(FSTAR_EXE) $(FSTAR_FLAGS)
 
 %.fst-in %.fsti-in:
 	@echo $(FSTAR_CHILL_FLAGS)