configs: Add -lstdc++ to default.

This fixes the following error when trying to run glxinfo or glxgears
with swrast.

undefined symbol: __cxa_pure_virtual

configs/default

@@ -116,7 +116,7 @@ EGL_CLIENT_APIS = $(GL_LIB)
 
 # Library dependencies
 #EXTRA_LIB_PATH ?=
-GL_LIB_DEPS     = $(EXTRA_LIB_PATH) -lX11 -lXext -lm -lpthread -ltalloc
+GL_LIB_DEPS     = $(EXTRA_LIB_PATH) -lX11 -lXext -lm -lpthread -ltalloc -lstdc++
 EGL_LIB_DEPS    = $(EXTRA_LIB_PATH) -ldl -lpthread
 OSMESA_LIB_DEPS = $(EXTRA_LIB_PATH) -L$(TOP)/$(LIB_DIR) -l$(GL_LIB)
 GLU_LIB_DEPS    = $(EXTRA_LIB_PATH) -L$(TOP)/$(LIB_DIR) -l$(GL_LIB) -lm