Disable gflags include (#28451)

Summary:
Fixes the issue explained in #28446
It basically disabled the gflags include before configure can detect the header on the users system.

## Changelog

[iOS] [Fixed] - Fixed inability to build apps when gflags is installed

Pull Request resolved: #28451

Test Plan: Tested by installing gflags `brew install gflags` and verifying that apps build after.

Reviewed By: javache

Differential Revision: D30345352

Pulled By: sota000

fbshipit-source-id: 04c98d7ddebe6708057407c4b4bf3701434822a3

scripts/ios-configure-glog.sh

@@ -28,6 +28,10 @@ if [ -h "test-driver" ]; then
     rm test-driver
 fi
 
+# Manually disable gflags include to fix issue https://github.com/facebook/react-native/issues/28446
+sed -i '' 's/\@ac_cv_have_libgflags\@/0/' src/glog/logging.h.in
+sed -i '' 's/HAVE_LIB_GFLAGS/HAVE_LIB_GFLAGS_DISABLED/' src/config.h.in
+
 ./configure --host arm-apple-darwin
 
 cat << EOF >> src/config.h