since the prebuilts sysroot was deleted and auto-generated
at build time, we should add the linux porting modifications
from the origin prebuilt sysroot.
Signed-off-by: NCaoruihong <crh.cao@huawei.com>
Change-Id: Ib277e01709484facf367a4e073f8b286ebef9e78

it turns out that __SOFTFP__ does not indicate the ABI in use but
rather that fpu instructions are not to be used at all. this is
specified in ARM's documentation so I'm unclear on how I previously
got the wrong idea. unfortunately, this resulted in the 0.9.12 release
producing a dynamic linker with the wrong name. fortunately, there do
not yet seem to be any public toolchain builds using the wrong name.

the __ARM_PCS_VFP macro does not seem to be official from ARM, and in
fact it was missing from the very earliest gcc versions (around 4.5.x)
that added -mfloat-abi=hard. it would be possible on such versions to
perform some ugly linker-based tests instead in hopes that the linker
will reject ABI-mismatching object files, if there is demand for
supporting such versions. I would probably prefer to document which
versions are broken and warn users to manually add -D__ARM_PCS_VFP if
using such a version.

there's definitely an argument to be made that the fenv macros should
be exposed even in -mfloat-abi=softfp mode. for now, I have chosen not
to expose them in this case, since the math library will not
necessarily have the capability to raise exceptions (it depends on the
CFLAGS used to compile it), and since exceptions are officially
excluded from the ARM EABI, which the plain "arm" arch aims to
follow.

patch by nsz. I've tested it on an armhf machine and it seems to be
working correctly.

this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.

some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.