Support for musl libc in OpenWrt

[Florian Fainelli <florian@openwrt.org>]

Hi All,

Support for musl libc in OpenWrt has been added in revision r34314, this 
was tested against:

- X86 in VirtualBox
- X86_64 with UML
- ARM with the realview target

Note that the following issues are known:

- unable to complete libstdc++ build due to some missing declarations (WIP)
- MIPS and MIPSel ports are not functionnal (details below)
- PowerPC has not been tested at all due to lack of hardware/emulation 
target

I did not try yet to compile our entire set of packages besides the one 
pre-selected in trunk, so you will certainly encounter some breakage due 
to musl being more strict about header inclusions and declarations than 
uClibc and (e)glibc.

Have fun!
--
MIPS and MIPSel specific issues:

using qemu's binary emulation (qemu-mips[el]) against a statically 
linked binary works, a dynamic binary makes my host qemu segv. Using 
qemu-system-mips[el], the binary segfaults while being executed by the 
kernel. So far I have not had the time to debug this further.
--
Florian