Failing MPFR tests

[lzcunt]

Two tests in MPFR 4.2.1 fails:

FAIL: tfpif
===========

mpfr_fpif_export did not fail on a read only stream
mlibc warning: Failed to flush file before exit()
FAIL tfpif (exit status: 1)

FAIL: tsprintf
==============

mlibc: Unknown printf terminator '97'
In function operator(), file ../options/ansi/generic/stdio.cpp:81
__ensure(!"Illegal printf terminator") failed
FAIL tsprintf (exit status: 132)

The second issue is simply #1102, the first is fwrite() succeeding on a read-only stream.