Patch merged into coreboot/master: Makefile.inc: Explicitly set GNU11 as C language standard

the following patch was just integrated into master:
commit acbb70b810c6eb17e403c37fa2888b479e5b23a9
Author: Paul Menzel 
Date:   Tue Nov 29 10:30:44 2016 +0100

Makefile.inc: Explicitly set GNU11 as C language standard

Different compiler versions use a different C language standard by
    default.

GCC 4.9 uses GNU89 by default [1], while GCC 5.x uses GNU11 [2].

The discussion on the mailing list in thread *[RFC] Setting C99 by
    default* [3] resulted in the preference of C11, which results in build
    errors.

So explicitly set it to GNU11, which is also what the current coreboot
    toolchain with GCC 5.3 is using.

[1] https://gcc.gnu.org/onlinedocs/gcc-4.9.4/gcc/C-Dialect-Options.html
    [2] https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/Standards.html
    [3] https://www.coreboot.org/pipermail/coreboot/2016-November/082541.html

Change-Id: If1569618f8044925ff72dcf3543480b34d4f90d6
    Signed-off-by: Paul Menzel 
    Reviewed-on: https://review.coreboot.org/17636
    Reviewed-by: Julius Werner 
    Reviewed-by: Arthur Heymans 
    Tested-by: build bot (Jenkins)
    Tested-by: Raptor Engineering Automated Test Stand

See https://review.coreboot.org/17636 for details.

-gerrit