I can't reproduce the +1.5k increase

```
[dirbaio@mars radio-app]$ arm-none-eabi-size target/thumbv7em-none-eabihf/debug/hello
   text	   data	    bss	    dec	    hex	filename
   6756	     48	   1036	   7840	   1ea0	target/thumbv7em-none-eabihf/debug/hello
[dirbaio@mars radio-app]$ cargo +1.72 build --bin hello 
    Finished dev [optimized + debuginfo] target(s) in 0.05s
[dirbaio@mars radio-app]$ arm-none-eabi-size target/thumbv7em-none-eabihf/debug/hello
   text	   data	    bss	    dec	    hex	filename
   6348	     48	   1036	   7432	   1d08	target/thumbv7em-none-eabihf/debug/hello
[dirbaio@mars radio-app]$ cargo +1.73 build --bin hello 
    Finished dev [optimized + debuginfo] target(s) in 0.05s
[dirbaio@mars radio-app]$ arm-none-eabi-size target/thumbv7em-none-eabihf/debug/hello
   text	   data	    bss	    dec	    hex	filename
   6756	     48	   1036	   7840	   1ea0	target/thumbv7em-none-eabihf/debug/hello