[PATCH] testsuite: Make stdio-common/tst-printf-format-*-mem UNSUPPORTED if the mtrace output does not exist

[Maciej W. Rozycki]

On Sun, 26 Jan 2025, Xi Ruoyao wrote:

> When gawk was not built with MPFR, there's no mtrace output and those
> tests FAIL.  But we should make them UNSUPPORTED like other
> tst-printf-format-* tests in the case.

 I had in mind a more thorough rework of the Makefile rules here, but this 
is obviously better than nothing in the interim.  Thank you.

  Maciej