[cmake] Adding options for INSTALL and TEST (#964)

* [cmake] Adding GSL_INSTALL option

Not all consumers of GSL automatically want to have this install logic.

It's good practice to gate install logic behind an option.
For an example look at magic_enum:
https://github.com/Neargye/magic_enum/blob/master/CMakeLists.txt

If the client wants to install GSL they still can. But they should ask
for it by overriding GSL_INSTALL.

* Update cmake/guidelineSupportLibrary.cmake

added nl@eof

* Update CMakeLists.txt

* Update CMakeLists.txt

Co-authored-by: Juan Ramos <juanr0911@gmail.com>
Co-authored-by: Jordan Maples [MSFT] <49793787+JordanMaples@users.noreply.github.com>

tests/CMakeLists.txt

@@ -10,6 +10,10 @@ find_package(Git REQUIRED QUIET)
 # will make visual studio generated project group files
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
+if(IOS)
+  add_compile_definitions(GTEST_HAS_DEATH_TEST=1)
+endif()
+
 pkg_search_module(GTestMain gtest_main)
 if (NOT GTestMain_FOUND)
     configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)