[native supports-expr] docs changes (#16971)

docs/maintainers/control-files.md

@@ -138,6 +138,7 @@ The grammar for the supports expression uses standard operators:
 - `(expr)` - grouping/precedence
 
 The predefined expressions are computed from standard triplet settings:
+- `native` - `TARGET_TRIPLET` == `HOST_TRIPLET`
 - `x64` - `VCPKG_TARGET_ARCHITECTURE` == `"x64"`
 - `x86` - `VCPKG_TARGET_ARCHITECTURE` == `"x86"`
 - `arm` - `VCPKG_TARGET_ARCHITECTURE` == `"arm"` or `VCPKG_TARGET_ARCHITECTURE` == `"arm64"`

docs/maintainers/manifest-files.md

@@ -370,7 +370,7 @@ platform-expression =
 | platform-expression-and
 | platform-expression-or ;
 
-platform-expression-identifier = 
+platform-expression-identifier =
 | identifier-character, { identifier-character }, optional-whitespace ;
 
 platform-expression-simple =
@@ -396,6 +396,8 @@ Ands and ors are a list of `&` or `|` separated identifiers, negated expressions
 One may not mix `&` and `|` without parentheses for grouping.
 
 These predefined identifier expressions are computed from standard triplet settings:
+- `native` - `TARGET_TRIPLET` == `HOST_TRIPLET`;
+  useful for ports which depend on their own built binaries in their build.
 - `x64` - `VCPKG_TARGET_ARCHITECTURE` == `"x64"`
 - `x86` - `VCPKG_TARGET_ARCHITECTURE` == `"x86"`
 - `arm` - `VCPKG_TARGET_ARCHITECTURE` == `"arm"` or `VCPKG_TARGET_ARCHITECTURE` == `"arm64"`

docs/users/host-dependencies.md

@@ -57,3 +57,9 @@ else()
     # This is a cross build
 endif()
 ```
+
+## Host-only ports
+
+Some ports are host-only: script ports and tool ports are common examples.
+In this case, you can use the `"native"` supports expression to describe this.
+This supports expression is true when `TARGET_TRIPLET == HOST_TRIPLET`.