title: pkg-config error during Rust cross-compilation
body: <p>I am getting this error when I try to cross-compile some Rust; does anyone know what I should be doing?</p>
  <p>This happens when I run cargo build --target aarch64, I get:</p>
  <pre><code>Compiling glib-sys v0.10.1
  error: failed to run custom build command for `glib-sys v0.10.1`
  ...
  pkg-config has not been configured to support cross-compilation.
  
              
  
  Install a sysroot for the target platform and configure it via
  PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_PATH, or install a
  cross-compiling wrapper for pkg-config and set it via
  PKG_CONFIG environment variable.
  </code></pre>
  <p>I might have asked this before a year or so ago, but anyway I cannot find any answer. I have tried adding various lines to my Cargo.toml but nothing seems to help.</p>
  <p>The relevant part of Cargo.toml has:</p>
  <pre><code>[target.'cfg(target_os = &quot;android&quot;)'.dependencies]
  cairo = &quot;0.0.4&quot;
  freetype = &quot;0.7.0&quot;
  glib = &quot;0.14.2&quot;
  openssl = &quot;0.10.36&quot;
  openssl-sys = {version = &quot;0.9.66&quot;, features = [&quot;vendored&quot;]}
  </code></pre>
  <p>There is probably a one-line answer to this; can anyone help me please.</p>