[wimal] Fix installation and re-enable cctools

[sysroot] Roll back to use libc++-8

The newer version of libc++ static library is not compiled with -fPIC.

[cmake] Disable linking clang dylib

Fix clang resource header installation.

[cmake] Re-add ld64 targets

[sysroot] Copy compiler_rt libraries for osx

[sysroot] Copy compiler_rt libraries for ios.

- [sysroot] Change the default output path to `output`, and generate
`compiler_rt` and `sysroot` in its subdirectories.
- [gitignore] Update gitignore.
- [azure] Update the output path of `sysroot` tasks.

[sysroot] Install alsa,X11,EGL,GLES for linux.

[sysroot] Link libc++ statically on android.

[cmake] Enable LTO by default.

[azure] Build on macos for all targets.

- [azure] Create only xz tarballs.