try_compile: Add options to specify language standards

Give `try_compile` callers a way to control the `CXX_STANDARD`,
`CXX_STANDARD_REQUIRED`, and `CXX_EXTENSIONS` properties of the
generated test target (or the `C` equivalents) in order to compile a
test source for a particular language standard.

Issue: #16456

Help/command/try_compile.rst

@@ -35,7 +35,11 @@ Try Compiling Source Files
               [COMPILE_DEFINITIONS <defs>...]
               [LINK_LIBRARIES <libs>...]
               [OUTPUT_VARIABLE <var>]
-              [COPY_FILE <fileName> [COPY_FILE_ERROR <var>]])
+              [COPY_FILE <fileName> [COPY_FILE_ERROR <var>]]
+              [<LANG>_STANDARD <std>]
+              [<LANG>_STANDARD_REQUIRED <bool>]
+              [<LANG>_EXTENSIONS <bool>]
+              )
 
 Try building an executable from one or more source files.  The success or
 failure of the ``try_compile``, i.e. ``TRUE`` or ``FALSE`` respectively, is
@@ -82,6 +86,18 @@ The options are:
 ``OUTPUT_VARIABLE <var>``
   Store the output from the build process the given variable.
 
+``<LANG>_STANDARD <std>``
+  Specify the :prop_tgt:`C_STANDARD` or :prop_tgt:`CXX_STANDARD`
+  target property of the generated project.
+
+``<LANG>_STANDARD_REQUIRED <bool>``
+  Specify the :prop_tgt:`C_STANDARD_REQUIRED` or
+  :prop_tgt:`CXX_STANDARD_REQUIRED` target property of the generated project.
+
+``<LANG>_EXTENSIONS <bool>``
+  Specify the :prop_tgt:`C_EXTENSIONS` or :prop_tgt:`CXX_EXTENSIONS`
+  target property of the generated project.
+
 In this version all files in ``<bindir>/CMakeFiles/CMakeTmp`` will be
 cleaned automatically.  For debugging, ``--debug-trycompile`` can be
 passed to ``cmake`` to avoid this clean.  However, multiple sequential

Help/release/dev/try_compile-lang-std.rst

@@ -0,0 +1,5 @@
+try_compile-lang-std
+--------------------
+
+* The :command:`try_compile` command source file signature gained new options
+  to specify the language standard to use in the generated test project.