buildroot

musl: bump to 1.1.18

Patch 0002-arm-atomics-asm-with-new-binutils.patch is upstream as of
commit b261a24256792177a5f0531dbb25cc6267220ca5.

Patch 0003-Makefile-include-per-arch-Makefile-before-Makefile is
upstream as of commit 45ca5d3fcb6f874bf5ba55d0e9651cef68515395.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>