remove -pedantic flag from cmake

When building sac2c on different *UNIX distros, our use of vardic macros causes GCC to spit out tons and tons of warnings when using the -pedantic flag.

Compilers like Clang emulate this behavior but provide a flag to suppress the warnings: -Wno-gnu-zero-variadic-macro-arguments.

At somepoint, GCC adopted this flag but it seems not to be standard, as most distros (even with newer version of GCC) do not support this flag.

This commit removes the -pedantic flag from the build flags, this allows us to retain some of our macros without ill-effect. However this means that sac2c is not built to strictly conform to C standard (though -pedantic does not garantee this anyway). Given that most C compilers all share the same feature sets and extensions, it seems unnessicary to include this anymore.

We still use -pedantic in the SAC compiler flags.