[scripts] Get clang version from soong/scripts/get_clang_version.py

... instead of manually parsing soong/cc/config/global.go

Also hard-code clang_base in gdbclient.py to 'prebuilts/clang/host' as
it's unlikely to change in global.go.

Test: acov-llvm.py flush
Test: verify gdbclient.read_toolchain_config() in the interpreter
Change-Id: I28ed4416749edcd5d623598eb65eeb7891b657ae
2 files changed