The autoconf macro for GIR passes $CFLAGS to g-ir-scanner.
g-ir-scanner extends those flags with the system-default which
includes -D_FORTIFY_SOURCE=2. Probably it should not do that,
but if you disable optimization, this results in a compler warning
in "/usr/include/features.h" [1]
export CFLAGS='-O0'
# Happens both with clang or gcc.
#export CC=clang
git clean -fdx
./autogen.sh
make
Work around that by injecting -Wno-error to $CFLAGS when invoking
g-ir-scanner.
[1] Related: https://sourceware.org/bugzilla/show_bug.cgi?id=13979
f6272144e9