Fix libgui warnings

The warnings were being hidden by the use of -isystem to include
frameworks/native/include.

Bug: 31752268
Test: m -j
Merged-in: Idba8278bc0a73886ecb7978617854b433c0b5875
Change-Id: Idba8278bc0a73886ecb7978617854b433c0b5875
3 files changed