ARM: soft-fp NaN representation correction

ARM: soft-fp NaN representation correction

Commit 7d92b78723848ae616709eb8f0191ea067025b18 [Fix ARM NAN fraction
bits.] removed all the bits set from NANFRAC macros and, when propagated
to libgcc, regressed gcc.dg/torture/builtin-math-7.c on soft-fp arm-eabi
targets, currently ARMv6-M (`-march=armv6-m -mthumb') only.  This is
because when used to construct a NaN in the semi-raw mode, they now
build an infinity instead.  Consequently operations such as (Inf - Inf)
now produce Inf rather than NaN.  The change worked for the original
test case, posted with PR libgcc/60166, because division is made in the
canonical mode, where the quiet bit is set separately, from the fp
class.

This change brings the quiet bit back to these macros, making semi-raw
mode calculations produce the expected results again.