* introduce LazyPath.cwd_relative variant and use it for --zig-lib-dir. closes#12685
* move overrideZigLibDir and setMainPkgPath to options fields set once
and then never mutated.
* avoid introducing Build/util.zig
* use doc comments for deprecation notices so that they show up in
generated documentation.
* introduce InstallArtifact.Options, accept it as a parameter to
addInstallArtifact, and move override_dest_dir into it. Instead of
configuring the installation via Compile step, configure the
installation via the InstallArtifact step. In retrospect this is
obvious.
* remove calls to pushInstalledFile in InstallArtifact. See #14943
* rewrite InstallArtifact to not incorrectly observe whether a Compile
step has any generated outputs. InstallArtifact is meant to trigger
output generation.
* fix child process evaluation code handling of `-fno-emit-bin`.
* don't store out_h_filename, out_ll_filename, etc., pointlessly. these
are all just simple extensions appended to the root name.
* make emit_directory optional. It's possible to have nothing outputted,
for example, if you're just type-checking.
* avoid passing -femit-foo/-fno-emit-foo when it is the default
* rename ConfigHeader.getTemplate to getOutput
* deprecate addOptionArtifact
* update the random number seed of Options step caching.
* avoid using `inline for` pointlessly
* avoid using `override_Dest_dir` pointlessly
* avoid emitting an executable pointlessly in test cases
Removes forceBuild and forceEmit. Let's consider these additions separately.
Nearly all of the usage sites were suspicious.
Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:
* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change
