A64: Increase the margin for veneer checks.

BUG=v8:3168
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/171603008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19525 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/a64/macro-assembler-a64.h

@@ -2200,7 +2200,7 @@ class MacroAssembler : public Assembler {
  private:
   // We generate a veneer for a branch if we reach within this distance of the
   // limit of the range.
-  static const int kVeneerDistanceMargin = 2 * KB;
+  static const int kVeneerDistanceMargin = 4 * KB;
   int unresolved_branches_first_limit() const {
     ASSERT(!unresolved_branches_.empty());
     return unresolved_branches_.begin()->first;