Add libc++ headers from toolchain to host tests

Instead of building host tests with the host toolchain, use a prebuilt
toolhain instead. Add libc++ headers and library paths so that we
can test our ability to build Trusty (sans QEMU) hermetically. Also
switch to using the prebuilt lld linker so that the host does not
need to install binutils which may or may not support linking the
prebuilt libc++.

Test: # on a system/in an image with no C/C++ toolchain installed
build.py generic-arm32-debug generic-arm32-gicv3-test-debug   \
  generic-arm32-test-debug generic-arm32-test generic-arm32   \
  generic-arm64-debug generic-arm64-fuzz-test-debug           \
  generic-arm64-gicv3-test-debug generic-arm64-test-debug-inc \
  generic-arm64-test-debug generic-arm64-test generic-arm64
Bug: 199946160

Change-Id: I5a21837957364952200a10e339fabb5b0308414b
1 file changed