disable copy of shared librt for musl builds

package/librt/Makefile

@@ -41,7 +41,9 @@ INSTALL_STYLE:=		manual
 librt-install:
 ifeq ($(ADK_NATIVE),)
 	${INSTALL_DIR} ${IDIR_LIBRT}/$(ADK_TARGET_LIBC_PATH)
+ifeq ($(ADK_TARGET_LIB_MUSL),)
 	${CP} ${STAGING_TARGET_DIR}/lib/librt*.so* ${IDIR_LIBRT}/$(ADK_TARGET_LIBC_PATH)
 endif
+endif
 
 include ${TOPDIR}/mk/pkg-bottom.mk