merge bitcoin#25542: Use Link Time Optimization for Qt code on Linux

Author: kwvg

depends/packages/expat.mk

@@ -9,6 +9,7 @@ define $(package)_set_vars
   $(package)_config_opts += --disable-dependency-tracking --enable-option-checking
   $(package)_config_opts += --without-xmlwf
   $(package)_config_opts_linux=--with-pic
+  $(package)_cflags += -fno-lto
 endef
 
 define $(package)_config_cmds

depends/packages/qt.mk

@@ -152,6 +152,9 @@ $(package)_config_opts_linux += -fontconfig
 $(package)_config_opts_linux += -no-opengl
 $(package)_config_opts_linux += -no-feature-vulkan
 $(package)_config_opts_linux += -dbus-runtime
+ifneq ($(LTO),)
+$(package)_config_opts_linux += -ltcg
+endif
 $(package)_config_opts_arm_linux += -platform linux-g++ -xplatform bitcoin-linux-g++
 $(package)_config_opts_i686_linux  = -xplatform linux-g++-32
 ifneq (,$(findstring -stdlib=libc++,$($(1)_cxx)))