crt: tests: update t_tls1

Previously, this test would simply print an error message if incrementing
thread-local variable yielded unexpected results. Instead, exit with non-zero
to signal an error.

Update this test to use `_Thread_local` keyword added in C11 when compiling
this test in C11 (or later) mode.

Remove use of MSVC-specific `__declspec (thread)`; we do not compile our tests
with MSVC compiler.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>