Narrow error check for multiple .tar.bz2 prebuilts

Bug: http://b/111998531

The way build servers are set up, we may end up with the Windows package
in the --clang-package-path option.  Narrow the check to fail if there
are multiple Linux prebuilts.

Test: N/A
Change-Id: I86e81108b58283745d66b10279154d38b116935f

test_compiler.py

diff --git a/test_compiler.py b/test_compiler.py
index 1f65527..8978b33 100755
--- a/test_compiler.py
+++ b/test_compiler.py
@@ -306,7 +306,7 @@
 def extract_packaged_clang(package_path):
     # Find package to extract
     tarballs = [f for f in os.listdir(package_path) if \
-                    f.endswith('.tar.bz2')]
+                    f.endswith('.tar.bz2') and 'linux' in f]
     if len(tarballs) != 1:
         raise RuntimeError(
             'No clang packages (.tar.bz2) found in ' + package_path)