Test struct existance against sizeof() operator Instead of declaring an "unused-variable" or "unused-but-set-variable" structure. This avoid unexpected broken configurations when using something like: $ ./configure CFLAGS="-Wall -Wextra -Werror" It causes AC_COMPILE_IFELSE to fail and thus leading to a mismatch configuration (because the CFLAGS are passed to the macro).

Tech Note #7
Quick building for testing with LTM

EXTRALIBS=-ltommath CFLAGS="-g3 -DLTC_NO_ASM -DUSE_LTM -DLTM_DESC" make -j3 IGNORE_SPEED=1 test