app/internal: consolidate CFLAGS and move -Werror to #cgo directives

Signed-off-by: Elias Naur <mail@eliasnaur.com>

cmd/gogio/androidbuild.go

@@ -126,7 +126,6 @@ func compileAndroid(tmpDir string, tools *androidTools, bi *buildInfo) (err erro
 			"GOARCH="+a,
 			"CGO_ENABLED=1",
 			"CC="+clang,
-			"CGO_CFLAGS=-Werror",
 		)
 		builds.Go(func() error {
 			_, err := runCmd(cmd)

cmd/gogio/iosbuild.go

@@ -483,7 +483,6 @@ func iosCompilerFor(target, arch string) (string, []string, error) {
 	}
 	cflags := []string{
 		"-fembed-bitcode",
-		"-Werror",
 		"-arch", allArchs[arch].iosArch,
 		"-isysroot", sdkPath,
 		"-m" + platformOS + "-version-min=" + minIOSVersion,