Statically linking the binaries

Makefile

@@ -1,5 +1,12 @@
 CC      ?= cc
 CFLAGS  ?= -std=c99 -Wall -Wextra -O2
+# Static by default so dist/deck-engine and dist/interpreter-cli (and the
+# `package` tarball built from them) don't depend on the build machine's
+# glibc version at runtime - a binary linked against a newer glibc than a
+# user's system has refuses to run at all ("GLIBC_2.3x not found"), which
+# is exactly the kind of thing a downloaded release package must not hit.
+# Override with `LDFLAGS= make` if static libc/libm aren't available.
+LDFLAGS ?= -static
 LDLIBS  := -lm
 
 BUILD_DIR     := build
@@ -86,11 +93,11 @@ all: $(ENGINE_BINARY) $(INTERP_BINARY) images i18n scripts
 
 $(ENGINE_BINARY): $(ENGINE_OBJS) $(ENGINE_MAIN_OBJ)
 	@mkdir -p $(DIST_DIR)
-	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LDLIBS)
 
 $(INTERP_BINARY): $(INTERP_LIB_OBJS) $(INTERP_MAIN_OBJ) $(INTERP_TAROT_TEXT_OBJS)
 	@mkdir -p $(DIST_DIR)
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 # The HTML report expects card art at img/<file> next to deck-engine, so
 # every build refreshes a copy alongside it (cheap: 22 small JPEGs).
@@ -137,20 +144,20 @@ test: $(ENGINE_TEST_BINARY) $(SIGNIFICANCE_TEST_BIN) $(JSON_TEST_BIN) $(NARRATIV
 	./$(GUIDANCE_TEST_BIN)
 
 $(ENGINE_TEST_BINARY): $(ENGINE_OBJS) $(ENGINE_TEST_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LDLIBS)
 
 $(SIGNIFICANCE_TEST_BIN): $(OBJ_DIR)/$(INTERP_SRC_DIR)/significance.o $(SIGNIFICANCE_TEST_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 $(JSON_TEST_BIN): $(OBJ_DIR)/$(INTERP_SRC_DIR)/json.o $(OBJ_DIR)/$(INTERP_SRC_DIR)/reading_io.o $(JSON_TEST_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 $(NARRATIVE_TEST_BIN): $(OBJ_DIR)/$(INTERP_SRC_DIR)/narrative.o $(INTERP_TAROT_TEXT_OBJS) $(NARRATIVE_TEST_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 $(GUIDANCE_TEST_BIN): $(OBJ_DIR)/$(INTERP_SRC_DIR)/guidance.o $(OBJ_DIR)/$(INTERP_SRC_DIR)/significance.o \
                       $(INTERP_TAROT_TEXT_OBJS) $(GUIDANCE_TEST_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 $(OBJ_DIR)/%.o: %.c
 	@mkdir -p $(dir $@)