GN: Fix invalid configuration for Android GCC build.

The disabling of the sin,cos,sinf,cosf functions had the wrong
condition for GN. This fixes that and also makes the condition
in common.gypi a bit more readable.

BUG=
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1307633008 .

Cr-Commit-Position: refs/heads/master@{#9871}
2 files changed