try_compile: Add option to control type of target

Create a `CMAKE_TRY_COMPILE_TARGET_TYPE` option to specify use
of `add_library(... STATIC ...)` for the generated test project.
This will be useful for cross-compiling toolchains that cannot
link a binary without custom flags or scripts.

Help/variable/CMAKE_TRY_COMPILE_TARGET_TYPE.rst

@@ -0,0 +1,15 @@
+CMAKE_TRY_COMPILE_TARGET_TYPE
+-----------------------------
+
+Type of target generated for :command:`try_compile` calls using the
+source file signature.  Valid values are:
+
+``EXECUTABLE``
+  Use :command:`add_executable` to name the source file in the
+  generated project.  This is the default if no value is given.
+
+``STATIC_LIBRARY``
+  Use :command:`add_library` with the ``STATIC`` option to name the
+  source file in the generated project.  This avoids running the
+  linker and is intended for use with cross-compiling toolchains
+  that cannot link without custom flags or linker scripts.