"const_fn" feature has been removed

[vitasam]

Hi, building the project with a nightly toolchain causes this error:

   Compiling num-bigint v0.3.3
   Compiling itertools v0.9.0
   Compiling lock_api v0.3.4
error[E0557]: feature has been removed
  --> C:\Users\...\.cargo\registry\src\github.com-1ecc6299db9ec823\lock_api-0.3.4\src\lib.rs:91:42
   |
91 | #![cfg_attr(feature = "nightly", feature(const_fn))]
   |                                          ^^^^^^^^ feature has been removed
   |
   = note: split into finer-grained feature gates

Does it mean that const_fn is in a stable now?

[vitasam]

"const_fn" problem was solved by incrementing the version of linked_list_allocator to 0.9:
linked_list_allocator = { version = "0.9" }

But there is another problem:

bihf/release/deps/rscalc-201d8df9902ac16b" "--gc-sections" "-Tdmcp/stm32_program.ld"
  = note: rust-lld: error: duplicate symbol: __aeabi_d2f
          >>> defined at rscalc.b3b4f384-cgu.0
          >>>            /home/.../rscalc/target/thumbv7em-none-eabihf/release/deps/rscalc-201d8df9902ac16b.rscalc.b3b4f384-cgu.0.rcgu.o:(__aeabi_d2f)

[vitasam]

Fixed the DM42 build - it looks quite impressive on DM42 hardware