Update Makefile

Author: jonatanklosko

Makefile

@@ -1,6 +1,6 @@
 PRIV_DIR := $(MIX_APP_PATH)/priv
 NIF_PATH := $(PRIV_DIR)/libpythonx.so
-C_SRC = $(shell pwd)/c_src
+C_SRC := $(shell pwd)/c_src
 
 CPPFLAGS := -shared -fPIC -fvisibility=hidden -std=c++17 -Wall -Wextra -Wno-unused-parameter -Wno-comment
 CPPFLAGS += -I$(ERTS_INCLUDE_DIR) -I$(FINE_INCLUDE_DIR)
@@ -19,8 +19,8 @@ ifeq ($(TARGET_ABI),darwin)
 	CPPFLAGS += -undefined dynamic_lookup -flat_namespace
 endif
 
-SOURCES = $(wildcard $(C_SRC)/*.cpp)
-HEADERS = $(wildcard $(C_SRC)/*.hpp)
+SOURCES := $(wildcard $(C_SRC)/*.cpp)
+HEADERS := $(wildcard $(C_SRC)/*.hpp)
 
 all: $(NIF_PATH)
 	@ echo > /dev/null # Dummy command to avoid the default output "Nothing to be done"