Enable CMake LTO/IPO support (WITH_LTO option)

Makefiles already support an option to enable link time optimizations.
This is now also possible in CMake by using the WITH_LTO option.
It's turned on by default if the compiler supports these flags.
Note: LTO is part of the inter-procedural optimization (IPO).

Signed-off-by: Kai Buschulte <kai.buschulte@cedalo.com>

CMakeLists.txt

@@ -99,6 +99,17 @@ if(WITH_CJSON)
 	endif()
 endif()
 
+option(WITH_LTO "Build with link time optimizations (IPO) / interprocedural optimization (IPO) enabled." ON)
+if(WITH_LTO)
+	include(CheckIPOSupported)
+	check_ipo_supported(RESULT is_ipo_supported OUTPUT output)
+	if(is_ipo_supported)
+		set_property(TARGET common-options PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
+	else()
+		message(WARNING "LTO/IPO is not supported: ${output}")
+	endif()
+endif()
+
 # ========================================
 # Include projects
 # ========================================

ChangeLog.txt

@@ -158,6 +158,7 @@ Clients:
 Build:
 - Increased CMake minimal required version to 3.14, which is required for the
   preinstalled SQLite3 find module.
+- Add an CMake option `WITH_LTO` to enable/disable link time optimization.
 
 
 2.0.14 - 2021-11-17