Better password hiding, POSIX macro, updated header and BSD compatibility

Makefile

@@ -1,16 +1,16 @@
-CC = gcc
+CC = cc
 CFLAGS = -Wall -Wextra -std=c99 -O2
 LDFLAGS = -lsodium
+INCLUDES = -I/usr/include -I/usr/local/include -I/usr/pkg/include
+LIBS = -L/usr/lib -L/usr/local/lib -L/usr/pkg/lib
 BUILD_DIR = build
 PREFIX = /usr/local
 
 all: $(BUILD_DIR)/salty
 
-$(BUILD_DIR)/salty: salty.c pawstd.h | $(BUILD_DIR)
-	$(CC) $(CFLAGS) -o $@ salty.c $(LDFLAGS)
-
-$(BUILD_DIR):
+$(BUILD_DIR)/salty: salty.c pawstd.h
 	mkdir -p $(BUILD_DIR)
+	$(CC) $(CFLAGS) -o $@ salty.c $(INCLUDES) $(LIBS) $(LDFLAGS)
 
 clean:
 	rm -rf $(BUILD_DIR)