Document native library modifier syntax and the whole-archive modifier specifically

Author: petrochenkov

src/items/external-blocks.md

@@ -125,6 +125,15 @@ specifies the kind of library with the following possible values:
 
 The `name` key must be included if `kind` is specified.
 
+The optional `modifiers` argument is a way to specify linking modifiers for the
+library to link.
+Modifiers are specified as a comma-delimited string with each modifier prefixed
+with either a `+` or `-` to indicate that the modifier is enabled or disabled,
+respectively.
+Specifying multiple `modifiers` arguments in a single `link` attribute,
+or multiple identical modifiers in the same `modifiers` argument is not currently supported. \
+Example: `#[link(name = "mylib", kind = "static", modifiers = "+whole-archive")`.
+
 The `wasm_import_module` key may be used to specify the [WebAssembly module]
 name for the items within an `extern` block when importing symbols from the
 host environment. The default module name is `env` if `wasm_import_module` is
@@ -153,6 +162,16 @@ this to satisfy the linking requirements of extern blocks elsewhere in your
 code (including upstream crates) instead of adding the attribute to each extern
 block.
 
+#### Linking modifiers: `whole-archive`
+
+This modifier is only compatible with the `static` linking kind.
+Using any other kind will result in a compiler error.
+
+`+whole-archive` means that the static library is linked as a whole archive
+without throwing any object files away.
+
+More implementation details about this modifier can be found in [documentation for rustc].
+
 ### The `link_name` attribute
 
 The `link_name` attribute may be specified on declarations inside an `extern`
@@ -186,3 +205,4 @@ restrictions as [regular function parameters].
 [_Visibility_]: ../visibility-and-privacy.md
 [attributes]: ../attributes.md
 [regular function parameters]: functions.md#attributes-on-function-parameters
+[documentation for rustc]: https://doc.rust-lang.org/rustc/command-line-arguments.html#-l-link-the-generated-crate-to-a-native-library