Allow specifying tool path/prefix for tests with CROSS_COMPILE.
Allow specifying tool path/prefix for tests with CROSS_COMPILE.

CROSS_COMPILE environment variable is a common convention to specify the path
and/or prefix to cross compilation tools (e.g. ar, objcopy).

Test Plan:
dotest.py $DOTEST_OPTS -t -p 'TestBSDArchives.py|TestBreakpointCommandsFromPython.py|TestFormats.py|TestObjCDynamicValue.py'
All of these tests now compile successfully and pass running macosx -> linux
using a cross compilation toolchain prefixed by CROSS_COMPILE without requiring
changing your PATH. They still pass when run locally on macosx.

Differential Revision: http://reviews.llvm.org/D9072


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@235320 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb