The picolibc module can be built without thread local storage support if
desired. Allow that by using 'imply' instead of 'select'. However, when
using the toolchain picolibc, we assume that TLS will be enabled wherever
supported, so make sure we match by adding a 'select' for this case.
Signed-off-by: Keith Packard <keithp@keithp.com>
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