Reland of Pass -no-canonical-prefixes to clang by default.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 6a495cc2a82b8b2500a5c7c0c5398b7389c8f0a3..7296b78cf0c9f658dca03f1547a014f96d256242 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -435,6 +435,17 @@
   if (is_clang && is_linux && strip_absolute_paths_from_debug_symbols) {
     absolute_path = rebase_path("//.")
     cflags += [ "-fdebug-prefix-map=$absolute_path=." ]
+  }
+
+  # Tells the compiler not to use absolute paths when passing the default
+  # paths to the tools it invokes. We don't want this because we don't
+  # really need it and it can mess up the goma cache entries. It would
+  # be nice if it was on by default in clang, but it isn't.
+  #
+  # TODO(thakis): Figure out if this should be the default, and expose in
+  # clang-cl if not.
+  if (is_clang && !is_win && !is_nacl) {
+    cflags += [ "-no-canonical-prefixes" ]
   }
 
   # C++11 compiler flags setup.