[OE-core] [for-krogoth] Backport for libc != glibc

[Otavio Salvador]

Hello,

At O.S. Systems we are involved in some projects which uses musl as
libC. For those, we are doing the SDK for faster development and found
that it is currently broken on Krogoth.

Master branch has the need fixes. The fixes needed are
OE-Core:2b9ae0ab and OE-Core:fcaaabb4

commit 2b9ae0ab056e62290f2328aa0d4dd70e6f138759
Author: Khem Raj <raj.khem at gmail.com>
Date:   Wed May 11 10:35:40 2016 -0700

    musl: Create symlinks for stub libraries

    Some libraries e.g. libm.so are needed to be
    created so that SDKs built with distros which
    disable static librararies can have the stubs
    and since default linker script requires -lm
    this helps in compiling applications with SDK

    there are .a equivalents for these libraries
    but they do not land in SDKs when static libs
    are disabled distrowide

    Signed-off-by: Khem Raj <raj.khem at gmail.com>
    Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

commit fcaaabb401fffcda4db9a7d1f927a2a404e4776d
Author: Khem Raj <raj.khem at gmail.com>
Date:   Wed May 11 10:35:45 2016 -0700

   gcc-runtime, libgcc: Symlink c++ header and startup files in
target_triplet for SDK use

   We build SDKs such that gcc-cross-candian is built for only one
   target *-*-linux and then use -muclibc or -mmusl to let it compile
   code for other libc variants. This works fine when libc = glibc
   however it does not work for c++ programs when libc != glibc since
   there are c++ headers installed under ${includedir}/c++/${BINV}/${TARGET_SYS}
   which is fine when gcc-runtime and gcc-cross-candian uses same
--target options
   gxx includedir searches in right triplet, but it fails with musl/uclibc
   since gcc will look for glibc based triplet but gcc-runtime will install
   them under musl/uclibc triplet.

   This patch symlinks the musl/uclibc triplet to glibc triplet when
libc != glibc

   This fixes SDKs for musl/uclibc

   Signed-off-by: Khem Raj <raj.khem at gmail.com>
   Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

Backporting those, on top of current Krogoth branch, fixes the SDK
issues we had at the moment.

Could those be reviewed and queued for the next backport?

-- 
Otavio Salvador                             O.S. Systems
http://www.ossystems.com.br        http://code.ossystems.com.br
Mobile: +55 (53) 9981-7854            Mobile: +1 (347) 903-9750