chore: remove binaries before building them

This is required to avoid "permission denied" errors on Windows if the the file is already in use.

src/lean.mk.in

@@ -105,6 +105,8 @@ $(BIN_OUT)/$(BIN_NAME): $(addprefix $(TEMP_OUT)/,$(REL_OS)) | $(BIN_OUT)
 ifdef CMAKE_LIKE_OUTPUT
 	@echo "[    ] Linking $@"
 endif
+# on Windows, must remove binary before writing a new one (since the old one may be in use)
+	@rm -f $@
 ifdef PROFILE
 	\time -f "%U %S" $(LEANC) -o "$@" $^ $(LEANC_OPTS) $(LINK_OPTS) 2>&1 > /dev/null | awk '{ printf "C linking %fs\n", $$1 + $$2 }' > /dev/stderr
 else

src/stdlib.make.in

@@ -44,16 +44,20 @@ Lean: Init
 # we specify the precise file names here to avoid rebuilds
 ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libleanshared${CMAKE_SHARED_LIBRARY_SUFFIX}: ${LIB}/lean/libInit.a ${LIB}/lean/libLean.a ${LIB}/lean/libleancpp.a ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a
 	@echo "[    ] Building $@"
+# on Windows, must remove file before writing a new one (since the old one may be in use)
+	@rm -f $@
 	"${CMAKE_BINARY_DIR}/leanc.sh" -shared -o $@ ${LEANSHARED_LINKER_FLAGS} ${LEANC_OPTS}
 
 leanshared: ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libleanshared${CMAKE_SHARED_LIBRARY_SUFFIX}
 
 Lake:
-# must put lake in its own directory because of submodule, so must adjust relative paths...
+# lake is in its own subdirectory, so must adjust relative paths...
 	+"${LEAN_BIN}/leanmake" -C lake bin lib PKG=Lake BIN_NAME=lake${CMAKE_EXECUTABLE_SUFFIX} $(LEANMAKE_OPTS) LINK_OPTS='-lleanshared ${CMAKE_EXE_LINKER_FLAGS_MAKE_MAKE}' OUT="../${LIB}" LIB_OUT="../${LIB}/lean" OLEAN_OUT="../${LIB}/lean"
 
 ${CMAKE_BINARY_DIR}/bin/lean${CMAKE_EXECUTABLE_SUFFIX}: ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libleanshared${CMAKE_SHARED_LIBRARY_SUFFIX} $(LEAN_SHELL)
 	@echo "[    ] Building $@"
+# on Windows, must remove file before writing a new one (since the old one may be in use)
+	@rm -f $@
 	"${CMAKE_BINARY_DIR}/leanc.sh" $(LEAN_SHELL) -lleanshared ${CMAKE_EXE_LINKER_FLAGS_MAKE} ${LEAN_EXE_LINKER_FLAGS} ${LEANC_OPTS} -o $@
 
 lean: ${CMAKE_BINARY_DIR}/bin/lean${CMAKE_EXECUTABLE_SUFFIX}