toolchain: Override __INTN_C macros to match Zephyr stdint types

This commit overrides the toolchain internal `__INTN_C(value)` integer
constant macros to match the types defined by the `zephyr_stdint.h`
header.

For more details, refer to the GitHub issue #44199.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>