posix: options: POSIX_THREADS require a stack

`pthread_setspecific` requires a stack in order to allocate the
`struct pthread_key_data` data structure. On 64 bit systems this data
structure is 32 bytes, resulting in 160 bytes usage for the default 5
supported threads.

Signed-off-by: Jordan Yates <[email protected]>

Author: JordanYates

lib/posix/options/Kconfig.pthread

@@ -15,6 +15,9 @@ menuconfig POSIX_THREADS
 
 if POSIX_THREADS
 
+config HEAP_MEM_POOL_ADD_SIZE_POSIX_THREADS
+	def_int 256
+
 config POSIX_THREAD_THREADS_MAX
 	int "Maximum number of POSIX threads"
 	default 5