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
diff --git a/test_compiler.py b/test_compiler.py
index 35f34a5..8d67821 100755
--- a/test_compiler.py
+++ b/test_compiler.py
@@ -200,7 +200,7 @@
         env[compiler_wrapper.PREBUILT_COMPILER_PATH_KEY] = fallback_path
 
     env['LLVM_PREBUILTS_VERSION'] = 'clang-dev'
-    env['LLVM_RELEASE_VERSION'] = clang_version.short_version()
+    env['LLVM_RELEASE_VERSION'] = clang_version.long_version()
 
     # http://b/62869798, we need to invoke cpp-define-generator manually to
     # avoid potential build failure. This should be removed when