gyp: Always use pkg-config wrapper Calling pkg-config directly doesn't work when building with a sysroot image as it will looks for host libraries rather than those within the sysroot. BUG=chromium:569947 Change-Id: I6f3e63c1816cd9393110cb3060744a69a93c9a2e Reviewed-on: https://chromium-review.googlesource.com/318771 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tryjob-Request: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Sam Clegg <sbc@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>