Added -D_REENTRANT for vx builds.

config/CONFIG.Vx

@@ -86,6 +86,11 @@ ANSI = GCC
 CPLUSPLUS = $(CPLUSPLUS_$(TORNADO))
 LD_CXX = $(LD_$(CPLUSPLUS))
 
+#--------------------------------------------------
+# Override flags in CONFIG_COMMON
+GCC_DEP_CFLAGS = -D_REENTRANT
+G++_DEP_CFLAGS = -D_REENTRANT
+
 #--------------------------------------------------
 # Operating system flags
 OP_SYS_INCLUDES = -I$(VX_INCLUDE)