firmware: globally enable LTO.

This used to crash with earlier rustc versions, but doesn't anymore,
and gives significant speedup (e.g. 2x on test_dma_record_time).

artiq/firmware/Cargo.toml

@@ -3,4 +3,5 @@ members = ["bootloader", "runtime", "ksupport", "satman"]
 
 [profile.dev]
 incremental = false # incompatible with LTO
+lto = true
 debug = 2

artiq/firmware/bootloader/Makefile

@@ -7,8 +7,7 @@ all:: bootloader.bin
 
 .PHONY: $(RUSTOUT)/libbootloader.a
 $(RUSTOUT)/libbootloader.a:
-	$(cargo) --manifest-path $(BOOTLOADER_DIRECTORY)/Cargo.toml -- \
-		-Clto
+	$(cargo) --manifest-path $(BOOTLOADER_DIRECTORY)/Cargo.toml
 
 bootloader.elf: $(RUSTOUT)/libbootloader.a
 	$(link) -T $(BOOTLOADER_DIRECTORY)/bootloader.ld