build-support/meson: set crt-static for rustc

Just like we do in the Cargo setup hook, to have musl/static builds
work properly we need to explicitly set whether we want static builds
or not.  Rust's built-in target definitions are inconsistent — some
musl architectures default to static, and others don't.

Unfortunately it doesn't seem to be valid to break this list onto
multiple lines.

(cherry picked from commit e5da99075b)

pkgs/build-support/lib/meson.nix

@@ -27,7 +27,9 @@ let
 
     [binaries]
     llvm-config = 'llvm-config-native'
-    rust = ['rustc', '--target', '${stdenv.targetPlatform.rust.rustcTargetSpec}']
+    rust = ['rustc', '-C', 'target-feature=${
+      if stdenv.targetPlatform.isStatic then "+" else "-"
+    }crt-static', '--target', '${stdenv.targetPlatform.rust.rustcTargetSpec}']
     # Meson refuses to consider any CMake binary during cross compilation if it's
     # not explicitly specified here, in the cross file.
     # https://github.com/mesonbuild/meson/blob/0ed78cf6fa6d87c0738f67ae43525e661b50a8a2/mesonbuild/cmake/executor.py#L72