ARM: fixup tests to specify the target more explicitly

This changes the tests that were targeting ARM EABI to explicitly specify the
environment rather than relying on the default.  This breaks with the new
Windows on ARM support when running the tests on Windows where the default
environment is no longer EABI.

Take the opportunity to avoid a pointless redirect (helps when trying to debug
with providing a command line invocation which can be copy and pasted) and
removing a few greps in favour of FileCheck.