Makefile: Don't disable gcc's use-linker-plugin option

This option seems to be confusing ld's region usage checks (builds
that could fit in small chips are being reported as not fitting).  The
option was disabled back in commit 4e8674d5 because it showed worse
results.  However, recent versions of gcc seem to produce the same
results even if this option is enabled, so change the build to avoid
disabling that option on newer versions of gcc (those that have the
-ffat-lto-objects option - which is needed to ensure
compile_time_requests sections can be extracted with objcopy).

The PRU build is dependent on -fuse-linker-plugin, so enable that
option explicitly in its build.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

Makefile

@@ -1,6 +1,6 @@
 # Klipper build system
 #
-# Copyright (C) 2016-2020  Kevin O'Connor <kevin@koconnor.net>
+# Copyright (C) 2016-2025  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 
@@ -33,7 +33,8 @@ CFLAGS := -iquote $(OUT) -iquote src -iquote $(OUT)board-generic/ \
 		-std=gnu11 -O2 -MD -Wall \
 		-Wold-style-definition $(call cc-option,$(CC),-Wtype-limits,) \
     -ffunction-sections -fdata-sections -fno-delete-null-pointer-checks
-CFLAGS += -flto=auto -fwhole-program -fno-use-linker-plugin -ggdb3
+CFLAGS += -flto=auto -fwhole-program -ggdb3
+CFLAGS += $(call cc-option,$(CC),-ffat-lto-objects,-fno-use-linker-plugin)
 
 OBJS_klipper.elf = $(patsubst %.c, $(OUT)src/%.o,$(src-y))
 OBJS_klipper.elf += $(OUT)compile_time_request.o

src/pru/Makefile

@@ -8,6 +8,7 @@ dirs-y += lib/pru_rpmsg
 
 CFLAGS += -Os -minrt -mmcu=am335x.pru1
 CFLAGS += -Ilib/pru_rpmsg/include -Ilib/pru_rpmsg/include/am335x
+CFLAGS += -fno-use-linker-plugin
 
 CFLAGS_klipper.elf := $(filter-out -mmcu=%, $(CFLAGS))
 CFLAGS_klipper.elf += -Wl,-r -nostdlib -Wl,-T,src/pru/pru.lds