Add binary size regression tests

[v-thakkar]

The binary size of a program, compiled with opt-level=s, is tracked over time (per PR) and the CI fails if the binary size of the program regresses. The deadline for adding these tests is September 8, 2018.

[sekineh]

https://internals.rust-lang.org/t/llvm-tools-a-new-rustup-component-for-binary-inspection-objdump-nm-size-and-profiling-profdata/7830

[sekineh]

Of course GNU version is more easily accessible now:

sekineh@sekineh-VirtualBox:~/rustme5$ arm-none-eabi-size --version
GNU size (2.26-4ubuntu1+8) 2.26

[sekineh]

Library crates create .rlib file which is not easy to analyze because of the lack of tooling.
In addition, they are essentially compressed form of LLVM bitcodes. Not suitable for binary size checking!

• Tools for dumping information about .rlibs rust-lang/rust#25820

So we must use 1) binary crates or 2) custom main for binary size regression tests.

[jamesmunns]

@sekineh you could also try building a staticlib, which would create a standard .a file. However, I am not sure how it behaves if you have not exposed the symbols (e.g. with #[no_mangle] and/or pub extern). It might be worth a check though :)

[sekineh]

@jamesmunns
staticlib might increase the visibility of codes in target arch.
In that case, we could edit Cargo.toml using sed, etc.

[sekineh]

The past regression:

• Serious binary size regression on ARMv7-M on nightly-2018-02-11 rust-lang/rust#49260