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>

toolchain/toolchain-external/pkg-toolchain-external.mk

@@ -476,7 +476,7 @@ endef
 # With the musl C library, the libc.so library directly plays the role
 # of the dynamic library loader. We just need to create a symbolic
 # link to libc.so with the appropriate name.
-ifeq ($(BR2_TOOLCHAIN_EXTERNAL_MUSL),y)
+ifeq ($(BR2_TOOLCHAIN_EXTERNAL_MUSL):$(BR2_STATIC_LIBS),y:)
 ifeq ($(BR2_i386),y)
 MUSL_ARCH = i386
 else ifeq ($(BR2_ARM_EABIHF),y)