[PATCH] Make Clang::Driver/linker-opts.c safe on a bare-metal compiler

[Tim Northover]

Hi Rich,

> The Clang test Driver/linker-opts.c tests that the LIBRARY_PATH environment
> variable works as expected. This functionality is only available if Clang is
> configured as a linux toolchain, if clang is built as a bare-metal toolchain
> then LIBRARY_PATH is not expected to work.

The GCC documentation
(http://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html) seems
to imply it's actually dependent on native vs cross rather than
embedded vs Linux. This fits with a few cursory tests I've just done
on my toolchains.

In that case, both versions of the test would be wrong, but it looks
like there's an actual Clang bug too since clang without a --target
may not be native.

Tim.