Update Clang build script and gyp file for 3.8.0 version bump

base/base.isolate

Index: base/base.isolate
diff --git a/base/base.isolate b/base/base.isolate
index c7ba651ac71f0924cb9c0f25a66bc58a2aa89d0a..948c60045ff24213210f8f7c4c87fbd9559131eb 100644
--- a/base/base.isolate
+++ b/base/base.isolate
@@ -36,7 +36,9 @@
     ['OS=="win" and asan==1 and component=="shared_library"', {
       'variables': {
         'files': [
-          '../third_party/llvm-build/Release+Asserts/lib/clang/3.7.0/lib/windows/clang_rt.asan_dynamic-i386.dll',
+          # We only need x.y.z/lib/windows/clang_rt.asan_dynamic-i386.dll,
+          # but since the version (x.y.z) changes, just grab the whole dir.
+          '../third_party/llvm-build/Release+Asserts/lib/clang/',
         ],
       },
     }],