Refactor error printing.

src/backends/C/c_backend.ml

src/backends/C/c_backend_main.ml

src/causality.ml

src/compiler_common.ml

src/corelang.ml

src/corelang.mli

src/lusic.ml

src/lustreSpec.ml

src/main_lustre_compiler.ml

src/modules.ml

src/options.ml

src/scheduling.ml