Add -target-api N to llvm-rs-cc

Otherwise HelloComputeNDK compiled by r10c/r10d's llvm-rs-cc
(whose target-api is set to 21) may crash on device running API 19.

  E/bcinfo  (28302): Invalid API version: 21 is out of range ('11' - '19')
  E/RenderScript(28302): Failed to translate bitcode from version: 21
  E/rsC++   (28302): Internal error: Object id 0.

BUG=19093878
Also see http://stackoverflow.com/questions/28057049/targeting-pre-lollipop-devices-using-renderscript-from-ndk-c

Change-Id: I790bce551be957114a60986a9e4b9b9e9f9eeb67
1 file changed