This makes it so that when there is a tree of std.Build objects, only
one zig-cache is used (the top-level application) instead of polluting
package directories with zig-cache folders.
* Use std.Build.Cache.Directory instead of a string for storing the
cache roots and build roots.
* Set up a std.Build.Cache in build_runner.zig and use it in
std.Build.RunStep for avoiding redundant work.
This function is needed when a library exposes one of its own library
dependency's headers as part of its own public API.
Also, improve error message when a file system error occurs during
install file step.
The `zig build` command now makes `@import("@dependencies")` available
to the build runner package. It contains all the dependencies in a
generated file that looks something like this:
```zig
pub const imports = struct {
pub const foo = @import("foo");
pub const @"bar.baz" = @import("bar.baz");
};
pub const build_root = struct {
pub const foo = "<path>";
pub const @"bar.baz" = "<path>";
};
```
The build runner exports this import so that `std.build.Builder` can
access it. `std.build.Builder` uses it to implement the new `dependency`
function which can be used like so:
```zig
const libz_dep = b.dependency("libz", .{});
const libmp3lame_dep = b.dependency("libmp3lame", .{});
// ...
lib.linkLibrary(libz_dep.artifact("z"));
lib.linkLibrary(libmp3lame_dep.artifact("mp3lame"));
```
The `dependency` function calls the build.zig file of the dependency as
a child Builder, and then can be ransacked for its build steps via the
`artifact` function.
This commit also renames `dependency.id` to `dependency.name` in the
`build.zig.ini` file.
stage2: change logic for detecting whether the main package is inside
the std package. Previously it relied on realpath() which is not portable.
This uses resolve() which is how imports already work.
* stage2: fix cleanup bug when creating Module
* flatten lib/std/special/* to lib/*
- this was motivated by making main_pkg_is_inside_std false for
compiler_rt & friends.
* rename "mini libc" to "universal libc"
