buildroot

toolchain-external: skip ld-musl symlink on static build

Static build with external musl toolchain leaves a dangling symlink to
libc.so. Don't create that symlink on static build.

Cc: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit 7cfd40f2d90b7bbea1d6309145542f16ead58986)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>