#3204 Snapshot build infrastructure should complain about missing hostname.mk

[Philipp Klaus Krause]

When trying to build a snapshot, I accidentially got the name of the directory that is supposed to contain hostname.mk wrong.
I took me a long time to find out about the problem, as the snapshot build went all the way to configure sdcc, which then failed:

checking build system type... aarch64-unknown-freebsd13.0
checking host system type... aarch64-unknown-freebsd13.0
checking for gawk... no
checking for mawk... no
checking for nawk... nawk
checking version of the package... 4.1.2
checking for aarch64-unknown-freebsd13.0-gcc... gcc
checking whether the C compiler works... no

I was wondering what I might have to put into hostname.mk to make it work, but didn't suspect that my hostname.mk wasn't even being used.
Maybe diagnostics could be improved to better indicate such a problem?