Xcode: Add option to specify build system variant

Extend the `-T <toolset>` option to support a `buildsystem=` field with
the Xcode generator.  Add a `CMAKE_XCODE_BUILD_SYSTEM` variable to
inform project code about the selected build system variant.

1 files changed, 21 insertions, 2 deletions

diff --git a/Help/generator/Xcode.rst b/Help/generator/Xcode.rst
index d893ac5..c0745dc 100644
--- a/Help/generator/Xcode.rst
+++ b/Help/generator/Xcode.rst
@@ -5,9 +5,28 @@ Generate Xcode project files.
 
 This supports Xcode 5.0 and above.
 
-Toolset Selection
-^^^^^^^^^^^^^^^^^
+.. _`Xcode Build System Selection`:
+
+Toolset and Build System Selection
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 By default Xcode is allowed to select its own default toolchain.
 The :variable:`CMAKE_GENERATOR_TOOLSET` option may be set, perhaps
 via the :manual:`cmake(1)` ``-T`` option, to specify another toolset.
+
+This generator supports toolset specification using one of these forms:
+
+* ``toolset``
+* ``toolset[,key=value]*``
+* ``key=value[,key=value]*``
+
+The ``toolset`` specifies the toolset name.  The selected toolset name
+is provided in the :variable:`CMAKE_XCODE_PLATFORM_TOOLSET` variable.
+
+The ``key=value`` pairs form a comma-separated list of options to
+specify generator-specific details of the toolset selection.
+Supported pairs are:
+
+``buildsystem=<variant>``
+  Specify the buildsystem variant to use.
+  See the :variable:`CMAKE_XCODE_BUILD_SYSTEM` variable for allowed values.