standard C compiler compatibility

[jaromil]

For unknown reasons, cjit will not build correctly this command (zenroom build):

 /usr/local/bin/cjit -DCMAKE -I/home/jrml/devel/zenroom/lib/milagro-crypto-c/build/include -I/home/jrml/devel/zenroom/lib/milagro-crypto-c/include -Isrc -Ilib/lua54/src -Ilib/milagro-crypto-c/build/include -Ilib/milagro-crypto-c/include -Ilib/ed25519-donna -Wall -Wextra -fPIC -D'ARCH=LINUX' -DARCH_LINUX -Og -ggdb -DDEBUG=1 -Wall -Wextra -pedantic -DNDEBUG -o CMakeFiles/amcl_core.dir/src/ecdh_support.c.o -c /home/jrml/devel/zenroom/lib/milagro-crypto-c/src/ecdh_support.c

reproducible also in absence of the source: error occurs at the flag parsing stage.