[FS#1391] ld: unrecognized option '-specs=[...]/include/hardened-ld-pie.specs' when build with PIE with musl

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Drei Eck (dreieck) 

Attached to Project - OpenWrt/LEDE Project
Summary - ld: unrecognized option '-specs=[...]/include/hardened-ld-pie.specs' when build with PIE with musl
Task Type - Build Failure
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - When I build OpenWRT with the options
  CONFIG_PKG_ASLR_PIE=y
  CONFIG_BUSYBOX_DEFAULT_PIE=y
  CONFIG_BUSYBOX_CONFIG_PIE=y


build will fail after some time with
  mips-openwrt-linux-musl-ld: unrecognized option '-specs=[...]/include/hardened-ld-pie.specs'

Disabling this options mitigates this build error.

The build was carried out on a `git clone` with latest commit from 2018-02-24T11:24:20+01:00, commit hash 9a0cc49089.

To build, a `git clone` was used, then a previously generated config file by `make menuconfig` and `./scripts/diffconfig.sh` was copied over to `.config`.

The commands used to build from there were:
  make -j1 V=s defconfig
  make -j1 V=s download
  make -j1 V=s IGNORE_ERRORS=m 2>%1 | tee make.log

Attached you find:
  * The diffconfig file used,
  * the .config file used (generated after a `make defconfig`),
  * the last parts of the output of `make -j1 V=s IGNORE_ERRORS=m 2>&1`.

The hardware I tried to build for is
  CONFIG_TARGET_lantiq=y
  CONFIG_TARGET_lantiq_xway=y
  CONFIG_TARGET_lantiq_xway_DEVICE_arcadyan_arv752dpw22=y

The toolchain (`staging_dir/toolchain-*`) is `mips_24kc_gcc-5.5.0_musl`.

Build is carried out on a x86_64 Arch Linux machine.


One or more files have been attached.

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1391