toolchain-funcs.eclass: softfloat detection, bug #666896

toolchain-funcs.eclass: softfloat detection, bug #666896

commit 921cb9c10de4d237924a61a1c27f914dfb479a64
"toolchain-funcs.eclass: Update tc-is-softfloat for new ARM tuples"
changed autodetection of mst 'arm*' targets from from 'no'
to 'yes'.

It is incorrect at least for bare-metal targets that tend
to pass their taget defaults.

Bug #666896 is one example example command:
    # crossdev -s1 \
        --env 'EXTRA_ECONF="--with-multilib-list=rmprofile"' \
        arm-none-eabi

rmprofile one of special cases for gcc as it explicitky does
not myx with any arch-specific options and --with-float=soft
breaks it:

    Error: You cannot use any of --with-arch/cpu/fpu/float/mode
    with --with-multilib-list=rmprofile

The immediate fix is to restore initial autodetection for bare-metal
targets.

Reported-by: Eugene Bright
Closes: https://bugs.gentoo.org/666896
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>