Forward the OpenWrt TARGET_LDFLAGS to the linker of the fw_printenv tool.
In addition also use the more standard make invocation script.
With this change the fw_printenv tool is built with PIE and Full RELRO
support when activated globally in OpenWrt.
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
(cherry picked from commit b7b2be0b268ced260ca8df84be1b0d469aaf6e38)