By running make compile-commands a `compile_commands.json` in the RIOT base
directory. With the environment variable `COMPILE_COMMANDS` the path of
this file can be changed to a custom location.
The `compile_commands.json` will contain the exact compile command, but
as additional flag `-I/usr/$(TARGET)/include` is added to work around
`clangd` not being able to locate the newlib system headers. The
additional includes can be overwritten using the environment variable
`COMPILE_COMMANDS_EXTRA_INCLUDES`.
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