The option is disabled by default.
configure.ac:
Add --enable-lto option to the configure script to enable LTO/LTCG.
scripts/mgnuc.in:
scripts/ml.in:
Pass LTO options to the C compiler/linker.
compiler/compile_target_code.m:
compiler/options.m:
scripts/Mercury.config.in:
Add internal options to specify C compiler and linker LTO/LTCG flags.