Add fPIE flag
Add fPIE flag

libvboot_host.a is needed by metrics, compiled in platform's gyp/ninja system.
All platform executables need to be position independent so we need
libvboot_host.a to be position independent too.

BRANCH=None
BUG=chromium:389742
TEST=Unittests.
TEST=Build vboot_reference and metrics, metrics compiles.
TEST=Build coreboot on a rambi, the compilation succeeds.
TEST=trybot run on daisy, link, duck, rambi and x86-mario.

Change-Id: I4b761d9435c35e3d3fcae2efc72fcaed7fc746a6
Reviewed-on: https://chromium-review.googlesource.com/206055
Reviewed-by: Aaron Durbin <af0622ab041e8b0f8e5819838dcc93898196e71f@chromium.org>
Tested-by: Bertrand Simonnet <40b502b5e65d48aef27fb03889d41481051706c5@chromium.org>
Commit-Queue: Bertrand Simonnet <40b502b5e65d48aef27fb03889d41481051706c5@chromium.org>

acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,coreboot/vboot,coreboot/vboot