Invoke the wrapped compiler with the wrapper's invocation path

Bug: http://b/37407093

Test: Following command uses relative paths in clang{,++}.real
invocation and the -resource-dir argument:
    prebuilts/clang/host/linux-x86/clang-3859424/bin/clang -no-canonical-prefixes -E -v -xc /dev/null -o /dev/null

Change-Id: Ib1dc4b1b4b66536f6dc42678f6f0fe2c52e2562c
2 files changed