build: add a config knob to enable LTO for all packages

This enables LTO for all packages which haven't opted-out.

Signed-off-by: Andre Heider <[email protected]>

config/Config-build.in

@@ -152,6 +152,13 @@ menu "Global build settings"
 		  garbage collection capabilites.
 		  Packages can choose to opt-out via setting PKG_BUILD_FLAGS:=no-gc-sections
 
+	config USE_LTO
+		bool
+		prompt "Use the link-time optimizer for all packages (EXPERIMENTAL)"
+		help
+		  Adds LTO flags to the CFLAGS and LDFLAGS.
+		  Packages can choose to opt-out via setting PKG_BUILD_FLAGS:=no-lto
+
 	config IPV6
 		def_bool y
 

include/package.mk

@@ -56,7 +56,7 @@ ifeq ($(call pkg_build_flag,gc-sections,$(if $(CONFIG_USE_GC_SECTIONS),1,0)),1)
   TARGET_CXXFLAGS+= -ffunction-sections -fdata-sections
   TARGET_LDFLAGS+= -Wl,--gc-sections
 endif
-ifeq ($(call pkg_build_flag,lto,0),1)
+ifeq ($(call pkg_build_flag,lto,$(if $(CONFIG_USE_LTO),1,0)),1)
   TARGET_CFLAGS+= -flto=auto -fno-fat-lto-objects
   TARGET_CXXFLAGS+= -flto=auto -fno-fat-lto-objects
   TARGET_LDFLAGS+= -flto=auto -fuse-linker-plugin