fix build on linux

should fix benoitc/barrel#1

c_src/Makefile

@@ -24,6 +24,7 @@ else ifeq ($(UNAME_SYS), Linux)
 	CC ?= gcc
 	CFLAGS ?= -O3 -std=c99 -finline-functions -Wall -Wmissing-prototypes
 	CXXFLAGS ?= -O3 -finline-functions -Wall
+	LDFLAGS ?= -lstdc++
 endif
 
 CFLAGS += -fPIC -I$(ERTS_INCLUDE_DIR) -I$(ERL_INTERFACE_INCLUDE_DIR)