Set LLVM_RELEASE_VERSION to the long version name

Bug: http://b/28196329

The runtimes are installed in the lib64/clang/<long_version> with
https://android-review.googlesource.com/#/c/toolchain/llvm/+/489318/,
Use long version so the right prebuilts get exported in the
aosp-master-plus-llvm build.

Test: test_compiler.py in aosp-master-plus-llvm branch
Change-Id: I89b3a3fa8347724f7053debad3cbcca715873a2a
1 file changed