adds new warnings to Android build (1/2)

The following warnings have been turned on, and turned on as errors:

-Wbool-operation
-Wimplicit-int-float-conversion
-Wint-in-bool-context
-Wstring-compare
-Wstring-plus-int
-Wxor-used-as-pow

Test: no extra tests necessary

Change-Id: Ic8ab26de9e5323e9b81ad79eef787abfb264848c