configure fails to detect gcc intrinsic for me. Example:

TEST_BUILTIN(__builtin_clz, 23)

will generate

configure:61584: checking for __builtin_clz configure:61608: /home/nilsson/pike/build/linux-3.19.0-25-generic-x86_64/smartlink gcc -o conftest -g -fvisibility=hidden -O3 -pipe -ggdb -fvar-tracking-assignments -funswitch-loops -m64 -mrdrnd conftest.c >&5 configure:61608: $? = 0 configure:61618: result: 9961pike_cv_builtin___builtin_clz

I.e. one level too much quoting. I'm not sure what the correct portable fix is though.