Makefile: Error on TOOLCHAIN=gcc-4.9

GCC 4.9 has been removed from the AOSP repo. We marked it deprecated
a while back but now it really doesn't work.

Bug: 193407077
Test: TOOLCHAIN=gcc-4.9 make linux_image
Change-Id: I2fe9838b4f87919867adc5c61084ce68c0af7962
1 file changed
tree: 4f01fc1a13836adbb04557b9bec1c06415838533
  1. aarch64/
  2. crosvm/
  3. cuttlefish/
  4. kvm-unit-tests/
  5. common.inc
  6. Makefile