[Patch,ld] Support cflags, ldflags from board description file in ld tests

[Vidya Praveen]

Hello,

This patch enables the ld regression test scripts to use ldflags and cflags
from the board description file. However, these are used only when the tests
makes use of default_ld_link or default_ld_simple_link or default_ld_compile
eventually.

Tested for aarch64-one-elf, arm-none-eabi, arm-none-linux-gnueabihf and
x86_64-unknown-linux-gnu.

OK for trunk?

Cheers
VP.

ld/testsuite/ChangeLog:

2013-12-11  Vidya Praveen  <vidyapraveen@arm.com>

        * lib/ld-lib.exp (default_ld_link): Use ldflags from board description
        file.
        (default_ld_simple_link): Likewise.
        (default_ld_compile): Use cflags from board description file.