buildgcc: Update GCC, Binutils, GMP, MPFR, GDB, IASL and LLVM

- GCC gets updated from 5.2.0 to 6.3.0:
gcc-6.3.0_riscv.patch is a diff between 5fcb8c4 and 173684b in
riscv-gcc, and it needs gcc-6.3.0_memmodel.patch.

- Binutils goes from 2.26.1 to 2.28:
There is a build error for MIPS gold so I add patch for it.

- GMP gets a bump from 6.1.0 to 6.1.2
- MPFR is updated from 3.1.4 to 3.1.5
- GDB is upgraded from 6.1.1 to 6.1.2
- IASL is changed from 20160831 to 20161222
- LLVM is changed from 3.8.0 to 3.9.1

Change-Id: I20fea838d798c430d8c4d2cc6b07614d967c60c5
Signed-off-by: Iru Cai <mytbk920423@gmail.com>
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/17189
Tested-by: build bot (Jenkins)

util/crossgcc/patches/gdb-7.12_amd64.patch

@@ -0,0 +1,15 @@
+diff -urN gdb-7.12.orig/gdb/configure.tgt gdb-7.12/gdb/configure.tgt
+--- gdb-7.12.orig/gdb/configure.tgt	2016-02-09 19:19:39.000000000 -0800
++++ gdb-7.12/gdb/configure.tgt	2016-04-21 17:42:32.628433139 -0700
+@@ -681,6 +681,11 @@
+ 			i387-tdep.o i386bsd-tdep.o i386obsd-tdep.o \
+ 			obsd-tdep.o bsd-uthread.o solib-svr4.o"
+ 	;;
++x86_64-*-*)
++	# Target: amd64
++	gdb_target_obs="amd64-tdep.o i386-tdep.o i387-tdep.o"
++	;;
++
+ xtensa*-*-linux*)	gdb_target=linux
+ 	# Target: GNU/Linux Xtensa
+ 	gdb_target_obs="xtensa-tdep.o xtensa-config.o xtensa-linux-tdep.o \