stm32f4discovery/testlibcxx: Enable tls to fix build error.

CXX:  libcxx/src/filesystem/directory_iterator.cpp libcxx/src/thread.cpp:123:2: error: #error "Thread.cpp needs to enable config of CONFIG_TLS_TASK_NELEM," " and CONFIG_TLS_TASK_NELEM > 0, please enable it"
  123 | #error "Thread.cpp needs to enable config of CONFIG_TLS_TASK_NELEM," \
      |  ^~~~~

Signed-off-by: cuiziwei <[email protected]>

Author: cuiziweizw

boards/arm/stm32/stm32f4discovery/configs/testlibcxx/defconfig

@@ -42,7 +42,8 @@ CONFIG_STM32_JTAG_SW_ENABLE=y
 CONFIG_STM32_USART2=y
 CONFIG_SYMTAB_ORDEREDBYNAME=y
 CONFIG_SYSTEM_NSH=y
-CONFIG_TLS_NELEM=4
+CONFIG_TLS_NELEM=16
+CONFIG_TLS_TASK_NELEM=8
 CONFIG_USART2_RXBUFSIZE=128
 CONFIG_USART2_SERIAL_CONSOLE=y
 CONFIG_USART2_TXBUFSIZE=128