Update Clang build script and gyp file for 3.8.0 version bump

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index e051e88fa0714ec266e58834fac47b7cb3c61ea8..ef7372905f89cbf6af05bcd3753d5743251ea7a4 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -5827,13 +5827,13 @@
                       # invoked via /fallback. This is critical for using macros
                       # like ASAN_UNPOISON_MEMORY_REGION in files where we fall
                       # back.
-                      '<(DEPTH)/<(make_clang_dir)/lib/clang/3.7.0/include_sanitizer',
+                      '<(DEPTH)/<(make_clang_dir)/lib/clang/<!(python <(DEPTH)/tools/clang/scripts/update.py --print-clang-version)/include_sanitizer',
                     ],
                   },
                   'VCLinkerTool': {
                     'AdditionalLibraryDirectories': [
                       # TODO(hans): If make_clang_dir is absolute, this breaks.
-                      '<(DEPTH)/<(make_clang_dir)/lib/clang/3.7.0/lib/windows',
+                      '<(DEPTH)/<(make_clang_dir)/lib/clang/<!(python <(DEPTH)/tools/clang/scripts/update.py --print-clang-version)/lib/windows',
                     ],
                   },
                   'target_conditions': [