don't overwrite SPC_CMD_VAR_FRANKENPHP_XCADDY_MODULES unconditionally (#2135)

fixes #2134

Signed-off-by: Marc <m@pyc.ac>

Author: henderkes

build-static.sh

@@ -198,7 +198,9 @@ else
 	SPC_CMD_VAR_PHP_MAKE_EXTRA_CFLAGS="${SPC_CMD_VAR_PHP_MAKE_EXTRA_CFLAGS} -fPIE -fstack-protector-strong -O2 -w -s"
 fi
 export SPC_CMD_VAR_PHP_MAKE_EXTRA_CFLAGS
-export SPC_CMD_VAR_FRANKENPHP_XCADDY_MODULES="--with github.com/dunglas/mercure/caddy --with github.com/dunglas/vulcain/caddy --with github.com/dunglas/caddy-cbrotli"
+if [ -z "$SPC_CMD_VAR_FRANKENPHP_XCADDY_MODULES" ]; then
+	export SPC_CMD_VAR_FRANKENPHP_XCADDY_MODULES="--with github.com/dunglas/mercure/caddy --with github.com/dunglas/vulcain/caddy --with github.com/dunglas/caddy-cbrotli"
+fi
 
 # Build FrankenPHP
 ${spcCommand} doctor --auto-fix