Gentoo install script — build newlib with nano USE flag

[waffle87]

Description

As title. Without, the following linking error occurs:

Linking: .build/handwired_onekey_proton_c_default.elf                                               [ERRORS]
 |
 | /usr/libexec/gcc/arm-none-eabi/ld: cannot find -lg_nano: No such file or directory
 | /usr/libexec/gcc/arm-none-eabi/ld: cannot find -lc_nano: No such file or directory
 | collect2: error: ld returned 1 exit status
 |
gmake[1]: *** [builddefs/common_rules.mk:267: .build/handwired_onekey_proton_c_default.elf] Error 1
Make finished with errors
gmake: *** [Makefile:414: handwired/onekey/proton_c:default] Error 1

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).