Error building program using gcc plugin from linux kernel source tree

Question

I am trying to use a grsecurity gcc plugin that I found on their unofficial linux kernel source tree (the respectre_plugin/ one). My GCC version is 4.7, I modified scripts/gcc-plugins/Makefile to make it compile the plugin, and I built it with the root Makefile using make gcc-plugins, that shows no error. Then, when I try to compile a C file that has a Spectre-like flaw, I got the following build error:

file.c:36:31: error: array_index_mask_nospec is not defined

This function is defined in respectre_plugin/respectre_plugin.c, and I have no idea why I've got this strange build error, if anyone knows about it... My build invocation is the following:

gcc -Wall -Wextra -std=c99 -fplugin=/path/to/respectre_plugin.so -c file.c -o file.o

Thanks for any help !