cmake: Declare toolchain support for thread local storage

The Zephyr SDK toolchains all enable TLS, so add a Kconfig setting
which reports this to the Zephyr build. This will allow the
explicit zephyr toolchain variant check in Zephyr's kernel/Kconfig to
eventually be removed.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

cmake/zephyr/Kconfig

@@ -3,3 +3,7 @@
 config TOOLCHAIN_ZEPHYR_0_14
 	def_bool y
 	select HAS_NEWLIB_LIBC_NANO if (ARC || (ARM && !ARM64) || RISCV)
+
+config TOOLCHAIN_ZEPHYR_SUPPORTS_THREAD_LOCAL_STORAGE
+	def_bool y
+	select TOOLCHAIN_SUPPORTS_THREAD_LOCAL_STORAGE