pkcs11: fix undefined behavior in attribute initialization (compound literals)

[sahesaha]

Problem:
Incorrect attribute values are observed in test_create_destroy_session_objects,
CKA_TOKEN = 0xe0 (expected CK_FALSE / 0)
The issue appears with default toolchain optimizations, even though no explicit -O2 is set. It disappears when forcing -O0, indicating optimization-dependent undefined behavior.

Root cause
Attributes are initialized using compound literals, e.g.:
C&(CK_BBOOL){CK_FALSE}
These create temporary objects whose addresses are stored and reused.
Their lifetime and storage are not guaranteed, and under optimization the compiler may reuse or overlap them, leading to invalid values.

Why not fix via -O0
Disabling optimization is not a valid solution:

Hides undefined behavior instead of fixing it
Not portable across compilers/toolchains
Impacts performance in security-sensitive code

Fix
Replace compound literals with static variables having stable storage:
e.g. static const CK_BBOOL ck_false = CK_FALSE;

[sahesaha]

Hi @etienne-lms , could you review this PR?