Bump GCC to 5.3.0

There was one change required here: support for "MEMMODEL_SYNC_*".  This
very long  GCC post <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65697>
talks about the formalization of the C++ memory model.  It looks like
this is it to allow for some ARM stupidity where they can speculatively
issue some memory operations.

As far as I can tell, the right thing to do here is to just treat the
SYNC versions the same as the non-SYNC versions -- this is the same
thing ia64 and rs600 do.  I can't find "MEMMODEL_SYNC" anywhere else
interesting, so there might be some flag to set to avoid doing this, but
I couldn't find it.

Makefile.in

@@ -3,7 +3,7 @@ builddir := @abs_top_builddir@
 INSTALL_DIR := @prefix@
 
 PACKAGES := binutils gcc glibc newlib
-gcc_version := 5.2.0
+gcc_version := 5.3.0
 binutils_version := 2.25.1
 glibc_version := 2.22
 newlib_version := 2.2.0

gcc/gcc/config/riscv/sync.md

@@ -55,12 +55,15 @@
   switch (INTVAL (operands[1]))
     {
     case MEMMODEL_SEQ_CST:
+    case MEMMODEL_SYNC_SEQ_CST:
     case MEMMODEL_ACQ_REL:
       return "fence rw,rw";
     case MEMMODEL_ACQUIRE:
+    case MEMMODEL_SYNC_ACQUIRE:
     case MEMMODEL_CONSUME:
       return "fence r,rw";
     case MEMMODEL_RELEASE:
+    case MEMMODEL_SYNC_RELEASE:
       return "fence rw,w";
     default:
       gcc_unreachable();