don't opencode kauth_cred_get()

Fix ATHHAL_DEBUG by syncing HALDEBUG() with Atheros HAL code.

branches: 1.5.2; 1.5.6;
Retire varargs.h support. Move machine/stdarg.h logic into MI
sys/stdarg.h and expect compiler to provide proper builtins, defaulting
to the GCC interface. lint still has a special fallback.
Reduce abuse of _BSD_VA_LIST_ by defining __va_list by default and
derive va_list as required by standards.

support building as a module

branches: 1.3.4; 1.3.6; 1.3.8; 1.3.10;
NetBSD doesn't support alq(9) and hence ATHHAL_DEBUG_ALQ is unusable.
Nevertheless, remove reference to old binary HAL header file in the
ATHHAL_DEBUG_ALQ section.

branches: 1.2.2; 1.2.4;
Now that we compile the Atheros HAL from source we pass all the right
flags to the compiler so it obeys the same ABI as the rest of the kernel.
Remove the hacks used to work around the abi differences (using %s7 as
curlwp) intruduced for the binary hal.

branches: 1.1.2; 1.1.4; 1.1.6;
Import HAL's OS dependent code and config(9)'s interface header.

Retire varargs.h support. Move machine/stdarg.h logic into MI
sys/stdarg.h and expect compiler to provide proper builtins, defaulting
to the GCC interface. lint still has a special fallback.
Reduce abuse of _BSD_VA_LIST_ by defining __va_list by default and
derive va_list as required by standards.

branches: 1.1.2; 1.1.4; 1.1.8; 1.1.10; 1.1.16;
Import HAL's OS dependent code and config(9)'s interface header.

support building as a module

branches: 1.1.2; 1.1.4; 1.1.8; 1.1.10; 1.1.14; 1.1.16; 1.1.18; 1.1.20;
Import HAL's OS dependent code and config(9)'s interface header.