Fix LTO regressions in nightly toolchain

[ascjones]

Fix for use-ink/ink#391.

Recent nightly has broken since rust-lang/rust#71925 (see rust-osdev/cargo-xbuild#69 (comment))

• Upgrades version of cargo-xbuild which adds LTO flag to sysroot build: Set -Clinker-plugin-lto for the sysroot build rust-osdev/cargo-xbuild#71.
• Disables lto flag when generating metadata which fixes file not recognized: File format not recognized. rel: Add default [profile.release] values to Cargo.toml if not present #40

[riusricardo]

The build command is fixed but generating the metadata is broken.
I get a cc linker error.

flipper/target/release/deps/flipper.flipper.8f0qzq8t-cgu.0.rcgu.o: file not recognized: File format not recognized
          collect2: error: ld returned 1 exit status

EDIT: Same error as in the tests :(

[ascjones]

@riusricardo indeed I am working on troubleshooting this as we speak

[ascjones]

As a workaround you can comment out lto = true in your contract's Cargo.toml in order to generate the metadata. Remember to enable again when building the contract itself.

I'm working on doing this automatically but in the meantime this should suffice.

[ascjones]

@riusricardo could you try again now, and see if it works for you?

[riusricardo]

@ascjones everything is working again 🎉

[riusricardo]

👍