Enable LTO

shaves off ~10% of the code size which is very nice ... also some RAM, but we are not short on RAM in this case.

CMakeLists.txt

@@ -143,6 +143,7 @@ if(CMAKE_CROSSCOMPILING)
   #]]
 
   # limit the text section to 28K (32K - 4k reserved for the bootloader)
+  set_target_properties(firmware PROPERTIES INTERPROCEDURAL_OPTIMIZATION True)
   target_link_options(firmware PUBLIC -Wl,--defsym=__TEXT_REGION_LENGTH__=28K)
 
   # generate firmware.bin file

src/main.cpp

@@ -166,3 +166,9 @@ int main() {
     }
     return 0;
 }
+
+// make lto happy...
+extern "C" void __cxa_pure_virtual() {
+    while (1)
+        ;
+}