lookup table of errno macro names for logging

strerror(EINTR) gives us "Interrupted system call", but sometimes we really want "EINTR".

This is how the `errno` tool (from moreutils) generates the list of errno values.
They use $(CC) to scrape <errno.h> to generate their own header table.
The -dD flag is a debug switch to make gcc retain macro definitions in the -E source.
errnos.h:

echo "#include <errno.h>" > dump.c ;

gcc -E -dD dump.c | awk '/^#define E/ { printf "{\"%s\",%s},\n", $2, $2 }'