clang: Let `gclient sync` autoupdate clang on linux if clang has been downloaded before.

tools/clang/scripts/update.sh

Index: tools/clang/scripts/update.sh
diff --git a/tools/clang/scripts/update.sh b/tools/clang/scripts/update.sh
index a41809b04123a3b10eae9b6e6e34ef39348a4521..c000c3699fe2a1d5896c539d129c6e413a2a908f 100755
--- a/tools/clang/scripts/update.sh
+++ b/tools/clang/scripts/update.sh
@@ -42,7 +42,7 @@ while [[ $# > 0 ]]; do
     --help)
       echo "usage: $0 [--force-local-build] [--mac-only] [--run-tests] "
       echo "--force-local-build: Don't try to download prebuilt binaries."
-      echo "--mac-only: Do nothing on non-Mac systems."
+      echo "--mac-only: Do initial download only on Mac systems."
       echo "--run-tests: Run tests after building. Only for local builds."
       exit 1
       ;;
@@ -50,8 +50,14 @@ while [[ $# > 0 ]]; do
   shift
 done
 
-if [[ -n "$mac_only" ]] && [[ "${OS}" != "Darwin" ]]; then
-  exit 0
+# --mac-only prevents the initial download on non-mac systems, but if clang has
+# already been downloaded in the past, this script keeps it up to date even if
+# --mac-only is passed in and the system isn't a mac. People who don't like this
+# can just delete their third_party/llvm-build directory.
+if ! [ -d "${LLVM_BUILD_DIR}" ]; then

[Mark Mentovai, 2011/10/31 21:06:02]

Use [[ double ]] square brackets.

[(unused - use chromium), 2011/10/31 21:16:32]

Done.

+  if [[ -n "$mac_only" ]] && [[ "${OS}" != "Darwin" ]]; then

[Mark Mentovai, 2011/10/31 21:06:02]

Instead of wrapping an if instead of another if like this, why not use a single
if and && them together?

[(unused - use chromium), 2011/10/31 21:16:32]

Seemed clearer to me for some reason. Changed.

+    exit 0
+  fi
 fi
 
 # TODO(thakis): Remove this after Sept 29 2011. http://crbug.com/96722