Make sure that arm-linux-gnu is still the apcs-gnu ABI when we

use clang -cc1 matching the front end and backend. Fix up a couple
of tests that were testing aapcs for arm-linux-gnu.

The test that removes the aapcs abi calling convention removes
them because the default triple matches what the backend uses
for the calling convention there and so it doesn't need to be
explicitly stated - see the code in TargetInfo.cpp.

llvm-svn: 224491