I'm working on a build.zig file where I'm leveraging InstallRawStep but I'd like to change the install dir. This allows the install dir to be changd and also enhances InstallRawStep to add more options in the future by putting them into a struct with default values. This also removes the need for an extra addInstallStepWithFormat function in build.zig.
In 7e23b3245a I made -O flags to the
linker emit a warning that the argument does nothing. That was not
correct however; LLD does have some logic that does different things
depending on -O0, -O1, and -O2. It defaults to -O1, and it does less
optimizations with -O0 and more with -O2.
With this commit, e.g. `-Wl,-O1` is supported by the `zig cc` frontend,
and by default we pass `-O0` to LLD in debug mode, and `-O3` in release
modes.
I also fixed a bug in the LLD ELF linker line which was incorrectly
passing `-O` flags instead of `--lto-O` flags for LTO.
