_setup_env.sh: Prevent Clang sysroot detection for userprogs

Prevent Clang sysroot detection for userprogs by specifying a path known
not to contain a sysroot.

See also: https://lore.kernel.org/linux-kbuild/20220112224342.958358-1-quic_eberman@quicinc.com/

Test: Compare .config from BUILD_CONFIG=common/build.config.gki.aarch64 ./build/build.sh
Bug: 214127735
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Change-Id: I8c23755c3d5d1c7ef12de642659afdcfb3c1e380
(cherry picked from commit e5f575376c3abcbc0cafe58746407af68b976c49)
1 file changed