[vim] Check output_dir in ninja-build.vim.

This patch changes ninja-build.vim to check GYP_GENERATOR_FLAGS for
output_dir setting. The function to check the output directory is shared
between YouCompleteMe configuration and ninja-build.vim.

BUG=NONE

Review URL: https://codereview.chromium.org/685653002

Cr-Original-Commit-Position: refs/heads/master@{#301871}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d026bc969fce5167b30df795bd4bba4df2a282ee
3 files changed