gcc: arm: linux-eabi: fix handling of armv4 bx fixups when linking

gcc: arm: linux-eabi: fix handling of armv4 bx fixups when linking

The bpabi.h header already sets up defines to automatically use the
--fix-v4bx flag with the assembler & linker as needed, and creates a
default assembly & linker spec which uses those.  Unfortunately, the
linux-eabi.h header clobbers the LINK_SPEC define and doesn't include
the v4bx define when setting up its own.  So while the assembler spec
is retained and works fine to generate the right relocs, building for
armv4 targets doesn't invoke the linker correctly so all the relocs
get processed as if we had an armv4t target.

You can see this with -dumpspecs when configuring gcc for an armv4
target and using --with-arch=armv4:
$ armv4l-unknown-linux-gnueabi-gcc -dumpspecs |& grep -B 1 fix-v4bx
*subtarget_extra_asm_spec:
.... %{mcpu=arm8|mcpu=arm810|mcpu=strongarm*|march=armv4|mcpu=fa526|mcpu=fa626:--fix-v4bx} ...

With this fix in place, we also get the link spec:
$ armv4l-unknown-linux-gnueabi-gcc -dumpspecs |& grep -B 1 fix-v4bx
*link:
...  %{mcpu=arm8|mcpu=arm810|mcpu=strongarm*|march=armv4|mcpu=fa526|mcpu=fa626:--fix-v4bx} ...

And all my hello world tests / glibc builds automatically turn the
bx insn into the 'mov pc, lr' insn and all is right in the world.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@198438 138bc75d-0d04-0410-961f-82ee72b054a4