Support genrules with multiple tools

To allow genrules with more than one tool, rename the tool property to
tools and make it an array, replace $tool with $(location <label>),
and use $() for other variables for consistency.

Bug: 31948427
Test: compare build.ninja
Change-Id: I898d8e1f6fe9c8293dc7c2cddc26236f08303aad
(cherry picked from commit 75dd8795f0d97e8742366fa7af617b470a175ce3)
1 file changed