Allow multiple -arm-enable-ehabi and -arm-enable-ehabi-descriptors

Clang adds -arm-enable-ehabi and -arm-enable-ehabi-descriptors
unconditionally for Android.  This may fail when user also specify
"-mllvm -arm-enable-ehabi" or "-mllvm -arm-enable-ehabi-descriptors"
in the command line.  Fix to allow multiple occurrences.

Change-Id: Ia1194f2eecd5187e12f5a2a48ed9a30f5c8f1a1e