Add gn arg for passing --no-rosegment to lld

This is used as a workaround to get profiling using Valgrind working.

BUG=830706

Change-Id: Ie502f78681b686ea595c06255b7be712e32c8322
Reviewed-on: https://chromium-review.googlesource.com/1002921
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549304}

build/config/compiler/BUILD.gn

@@ -116,6 +116,11 @@ declare_args() {
 
   # Turn this on to have the compiler output extra timing information.
   compiler_timing = false
+
+  # Set to true to pass --no-rosegment to lld. This is a workaround
+  # for a KI issue in Valgrind,
+  # https://bugs.kde.org/show_bug.cgi?id=384727
+  ro_segment_workaround_for_valgrind = false
 }
 
 declare_args() {
@@ -636,6 +641,12 @@ config("compiler") {
     }
   }
 
+  # Pass flag to LLD to work around issue in Valgrind related to
+  # location of debug symbols.
+  if (use_lld && ro_segment_workaround_for_valgrind) {
+    ldflags += [ "-Wl,--no-rosegment" ]
+  }
+
   # Pass the same C/C++ flags to the objective C/C++ compiler.
   cflags_objc += cflags_c
   cflags_objcc += cflags_cc