[tlbuild] Solaris fails to process asy's Makefile

[Karl Berry]

    When I attempt to write portable scripts, do I have to consider
    anything which predates POSIX?

Later POSIX standards certainly include many features which cannot be
portably used, such as $(...) instead of `...`.  As for the earliest
POSIX sh standard, I'm not sure if there are problematic features.  If
it specifies -e as an operator for the builtin test, then yes, it does :).

In practice, Solaris /bin/sh is the problem.  (I suspect dash is more
featureful than Solaris sh, but I don't know it for a fact.)  Although
other proprietary vendor shells (AIX, etc.) have other (and worse)
problems, those systems are now so rare as to be ignorable.  All the
GNU/Linux and BSD systems have reasonable /bin/sh's by now, as far as I
know.

Here is a lengthy exhumation of various problems, mostly written in the
80s and 90s:
https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Portable-Shell.html

karl