Fix failure in printing/BUILD.gn when not using a sysroot. Without this change, gn gen fails with "cups-config not found: usr/bin/cups-config".
Fix failure in printing/BUILD.gn when not using a sysroot. Without this change, gn gen fails with "cups-config not found: usr/bin/cups-config".

BUG=504446

Review URL: https://codereview.chromium.org/1554383002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#367558}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk