gogio: [android] add CXX environment variable for cgo cross-compilation

Adds the CXX environment variable when building Android shared libraries
to ensure proper C++ compiler selection for cgo-enabled packages.

Signed-off-by: CoyAce <AkeyCoy@gmail.com>

gogio/androidbuild.go

@@ -232,6 +232,7 @@ func compileAndroid(tmpDir string, tools *androidTools, bi *buildInfo) (err erro
 			"GOARM=7", // Avoid softfloat.
 			"CGO_ENABLED=1",
 			"CC="+clang,
+			"CXX="+clang+"++",
 		)
 		builds.Go(func() error {
 			_, err := runCmd(cmd)