advapi32: Make sure not to return a credential with a NULL UserName field when a Mac Keychain doesn't have an account name attribute.

dbghelp: Revert commit ae1791b0 and correctly fix what this patch was trying to do.

Otherwise on Windows longjmp may want to mess with the exception frame.

Factorise out bits of the other tests so that the code is cleaner and 
can be re-used.

cryptdlg: Add stubs for CertTrustInit, CertTrustCertPolicy, CertTrustCleanup and CertTrustFinalPolicy.

Support the static and register keywords.

This consolidates externdef and constdef rules into one declaration rule.

Return a decl_spec_t structure from decl_spec rules so that the storage
class and type qualifiers can both be returned.