Improved logic for enabling LTO

CMake 3.9 added proper support for enabling LTO on all platforms, so we no
longer need to rely on our previous MSVC specific code.

CMakeLists.txt

@@ -2,7 +2,7 @@ if (TARGET Zycore)
     return()
 endif ()
 
-cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.9 FATAL_ERROR)
 
 project(Zycore VERSION 1.1.0.0 LANGUAGES C CXX)
 
@@ -127,7 +127,7 @@ target_include_directories("Zycore"
     PRIVATE "src")
 target_compile_definitions("Zycore" PRIVATE "_CRT_SECURE_NO_WARNINGS")
 zyan_set_common_flags("Zycore")
-zyan_maybe_enable_wpo_for_lib("Zycore")
+zyan_maybe_enable_wpo("Zycore")
 
 if (ZYAN_NO_LIBC)
     target_compile_definitions("Zycore" PUBLIC "ZYAN_NO_LIBC")

cmake/zyan-functions.cmake

@@ -34,16 +34,12 @@ function (zyan_set_source_group target)
 endfunction ()
 
 function (zyan_maybe_enable_wpo target)
-    if (ZYAN_WHOLE_PROGRAM_OPTIMIZATION AND MSVC)
-        set_target_properties("${target}" PROPERTIES COMPILE_FLAGS "/GL")
-        set_target_properties("${target}" PROPERTIES LINK_FLAGS_RELEASE "/LTCG")
+    if (ZYAN_WHOLE_PROGRAM_OPTIMIZATION)
+        set_property(TARGET "${target}" PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
     endif ()
 endfunction ()
 
+# deprecated alias for `zyan_maybe_enable_wpo`, for backward compatibility.
 function (zyan_maybe_enable_wpo_for_lib target)
-    if (ZYAN_WHOLE_PROGRAM_OPTIMIZATION AND MSVC)
-        set_target_properties("${target}" PROPERTIES COMPILE_FLAGS "/GL")
-        set_target_properties("${target}" PROPERTIES LINK_FLAGS_RELEASE "/LTCG")
-        set_target_properties("${target}" PROPERTIES STATIC_LIBRARY_FLAGS_RELEASE "/LTCG")
-    endif ()
+    zyan_maybe_enable_wpo("${target}")
 endfunction ()