This implements the XSI-compliant version of strerror_r() - as opposed
to the GNU-specific variant.
The function explicitly saves errno so as to not accidentally change it
with one of the calls to other functions.
According to POSIX.1 all error codes have to be distinct - with
the exception for EAGAIN and EWOULDBLOCK. Other libcs including
eglibc and newlib define EWOULDBLOCK as an alias for EAGAIN and
some software including OpenTTD expect this behavior.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
I dont know why we do a fast path in the Kernel, but not in Userspace
Also simplified the byte explosion in memset to "explode_byte"
it even seemed so, that we missed the highest byte when memseting something
