Use -ffunction-sections to build smaller binaries

[rustyrussell]

This gives us a 20% reduction in in-memory sizes for non-Rust binaries.

[Lagrang3]

If I don't build manually tools/lightning-hsmtool I get the following error

$ uv run make print-binary-sizes
User programs:
   text	   data	    bss	    dec	    hex	filename
2207578	   6736	   4928	2219242	 21dcea	lightningd/lightning_channeld
...
 180194	   2840	    296	 183330	  2cc22	cli/lightning-cli
4015976	 363400	  21760	4401136	 4327f0	lightningd/lightningd
size: 'tools/lightning-hsmtool': No such file
2057558	   6344	   4768	2068670	 1f90be	plugins/autoclean
...
2186875	   9280	   4704	2200859	 21951b	plugins/bookkeeper
177776820	5769632	 322872	183869324	af59f8c	(TOTALS)
make: *** [Makefile:1111: print-binary-sizes] Error 1

The problem is that ALL_PROGRAMS contain tools/hsmtool but not tools/lightning-hsmtool. The latter is instead found in BIN_PROGRAMS and it is a dependency of the make install target. A fix could be to make print-binary-sizes dependent on BIN_PROGRAMS as well.

diff --git a/Makefile b/Makefile
index 5c93e6145..4798fc59d 100644
--- a/Makefile
+++ b/Makefile
@@ -1106,7 +1106,7 @@ ccan-rune-rune.o: $(CCANDIR)/ccan/rune/rune.c
 ccan-rune-coding.o: $(CCANDIR)/ccan/rune/coding.c
        @$(call VERBOSE, "cc $<", $(CC) $(CFLAGS) -c -o $@ $<)
 
-print-binary-sizes: $(ALL_PROGRAMS) $(ALL_TEST_PROGRAMS)
+print-binary-sizes: $(ALL_PROGRAMS) $(ALL_TEST_PROGRAMS) $(BIN_PROGRAMS)
        @echo User programs:
        @size -t $(PKGLIBEXEC_PROGRAMS) $(filter-out tools/reckless,$(BIN_PROGRAMS)) $(PLUGINS)
        @echo All programs: