Sync build settings to XFA.
Sync build settings to XFA.

This matches some whitespace/ordering changes made to BUILD.gn on XFA branch.

TBR=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1410773007 .

DrAlexx/pdfium,andoma/pdfium,andoma/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,andoma/pdfium,andoma/pdfium