Document new function conan.tools.gnu.is_mingw()

reference/conanfile/tools/gnu.rst

@@ -14,5 +14,6 @@ conan.tools.gnu
    gnu/autotoolsdeps
    gnu/autotoolstoolchain
    gnu/autotools
+   gnu/mingw
    gnu/pkgconfigdeps
    gnu/pkgconfig

reference/conanfile/tools/gnu/mingw.rst

@@ -0,0 +1,27 @@
+.. _conan_tools_gnu_mingw:
+
+conan.tools.gnu.is_mingw()
+--------------------------
+
+Available since: `1.57.0 <https://github.com/conan-io/conan/releases/tag/1.57.0>`_
+
+.. code-block:: python
+
+    def is_mingw(conanfile):
+
+Check whether ``self.settings`` is a MinGW compiler.
+It returns ``True`` when host os is ``Windows`` and host compiler is ``gcc`` or ``clang``
+and ``compiler.runtime`` is not set, otherwise returns ``False``.
+When the ``compiler`` is empty, it returns ``False``.
+
+Parameters:
+
+- **conanfile**: ConanFile instance.
+
+.. code-block:: python
+
+    from conan.tools.gnu import is_mingw
+
+    def build(self):
+        if is_mingw(self):
+            # some logic to build with mingw