am ec97c3f0: Merge "asm/sigcontext.h is required to build unwind-dw2.c in gcc-4.9."

* commit 'ec97c3f0246680c77a2f9d72e0f1600f799e1754':
  asm/sigcontext.h is required to build unwind-dw2.c in gcc-4.9.