Make Clang plugins directory configurable for GCMole.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/13956027

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14374 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/gcmole/gcmole.lua

@@ -80,11 +80,16 @@ end
 -- Clang invocation
 
 local CLANG_BIN = os.getenv "CLANG_BIN"
+local CLANG_PLUGINS = os.getenv "CLANG_PLUGINS"
 
 if not CLANG_BIN or CLANG_BIN == "" then
    error "CLANG_BIN not set"
 end
 
+if not CLANG_PLUGINS or CLANG_PLUGINS == "" then
+   CLANG_PLUGINS = DIR
+end
+
 local function MakeClangCommandLine(plugin, plugin_args, triple, arch_define)
    if plugin_args then
      for i = 1, #plugin_args do
@@ -92,7 +97,7 @@ local function MakeClangCommandLine(plugin, plugin_args, triple, arch_define)
      end
      plugin_args = " " .. table.concat(plugin_args, " ")
    end
-   return CLANG_BIN .. "/clang -cc1 -load " .. DIR .. "/libgcmole.so"
+   return CLANG_BIN .. "/clang -cc1 -load " .. CLANG_PLUGINS .. "/libgcmole.so"
       .. " -plugin "  .. plugin
       .. (plugin_args or "")
       .. " -triple " .. triple