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

cc/config/global.go

@@ -53,6 +53,7 @@ var (
 		"-Werror=date-time",
 		"-Werror=pragma-pack",
 		"-Werror=pragma-pack-suspicious-include",
+		"-Werror=string-plus-int",
 		"-Werror=unreachable-code-loop-increment",
 	}
 
@@ -116,8 +117,13 @@ var (
 	}
 
 	noOverrideGlobalCflags = []string{
+		"-Werror=bool-operation",
+		"-Werror=implicit-int-float-conversion",
+		"-Werror=int-in-bool-context",
 		"-Werror=int-to-pointer-cast",
 		"-Werror=pointer-to-int-cast",
+		"-Werror=string-compare",
+		"-Werror=xor-used-as-pow",
 		// http://b/161386391 for -Wno-void-pointer-to-enum-cast
 		"-Wno-void-pointer-to-enum-cast",
 		// http://b/161386391 for -Wno-void-pointer-to-int-cast