CMakeLists,rust: fix compilation error

With the symbols present, this happened:

```
/usr/local/bin/arm-none-eabi-objcopy: not stripping symbol `memcpy' because it is named in a relocation
/usr/local/bin/arm-none-eabi-objcopy: not stripping symbol `memmove' because it is named in a relocation
/usr/local/bin/arm-none-eabi-objcopy: not stripping symbol `memset' because it is named in a relocation
```

Seems like in the updated Rust toolchain, the symbols are correctly
referenced and no workaround is needed.

In return, some other symbols now seem to clash, but only in
device-tests.

Author: benma

src/CMakeLists.txt

@@ -1,5 +1,6 @@
 # Copyright (c) 2015-2016 Lucas Betschart, Douglas J. Bakkum
 # Copyright 2019 Shift Cryptosecurity AG
+# Copyright 2020 Shift Crypto AG
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -449,8 +450,12 @@ foreach(type ${RUST_LIBS})
     RUSTC_BOOTSTRAP=1
     ${CARGO} build --manifest-path ${LIBBITBOX02_RUST_SOURCE_DIR}/Cargo.toml --features target-${type} --target-dir ${RUST_BINARY_DIR} ${RUST_CARGO_FLAG} ${RUST_TARGET_ARCH_ARG}
     # Rust packages stdlib functions which we must remove/weaken on the arm target
+    # Currently the removed symbols only clash in device-tests for some reason. Without this command, compiling device tests would result in errors like:
+    # Linking C executable ../../bin/fw_test_usb_cmd_process.elf
+    # /usr/local/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: /usr/local/bin/../lib/gcc/arm-none-eabi/8.2.1/thumb/v7e-m+fp/softfp/libgcc.a(_arm_addsubdf3.o): in function `__aeabi_dsub':
+    # (.text+0x8): multiple definition of `__aeabi_dsub'; ../../lib/libfirmware_rust_c.a(compiler_builtins-5829be534503bd8e.compiler_builtins.cthmhl66-cgu.175.rcgu.o):/cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.27/src/macros.rs:226: first defined here
     COMMAND
-    if test "x${RUST_TARGET_ARCH}" = "xthumbv7em-none-eabi" \; then ${CMAKE_OBJCOPY} -N memset -N memcpy -N memmove -W memcmp ${lib} \; fi
+    if test "x${RUST_TARGET_ARCH}" = "xthumbv7em-none-eabi" \; then ${CMAKE_OBJCOPY} -W __aeabi_dsub -W __aeabi_dadd -W__aeabi_i2d -W __aeabi_f2d -W __aeabi_dmul ${lib} \; fi
     COMMAND
     ${CMAKE_COMMAND} -E copy ${lib} ${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/lib${type}_rust_c.a
     BYPRODUCTS