Fix #346: GHA: CLANG started failing

Makefile

@@ -50,7 +50,8 @@ TEST_OBJ       := test/main
 SMOKE_TEST_OBJ := test/smoke
 
 CC        := g++
-CFLAGS    := -I$(SFML_DIR)/include -I./include -std=c++20 -pedantic -Wall -Wextra -Wshadow -Wwrite-strings -O2
+#!Note: not using := below, to give $(GHA_OLD_CLANG_WORKAROUND) a chance...:
+CFLAGS     = -I$(SFML_DIR)/include -I./include -std=c++20 $(GHA_OLD_CLANG_WORKAROUND) -pedantic -Wall -Wextra -Wshadow -Wwrite-strings -O2
 LDFLAGS   := $(LDFLAGS) -L$(SFML_DIR)/lib
 #!! This may also be needed on Debian (not on Ubuntu) -- but just compiled it on my WSL Bullseye without it, so WTF?? --:
 #!! LDFLAGS   := -pthread $(LDFLAGS)
@@ -151,3 +152,13 @@ mrproper: clean
 	-@rm $(TEST_EXE)
 	@echo "$(TERM_YELLOW)Removing$(TERM_NO_COLOR) $(SMOKE_TEST_EXE)"
 	-@rm $(SMOKE_TEST_EXE)
+
+
+#=============================================================================
+# Misc. workarounds...
+#
+
+# https://github.com/xparq/sfw/issues/346
+ifeq "$(CC)" "clang++"
+GHA_OLD_CLANG_WORKAROUND = -stdlib=libc++
+endif