[tarball] - add .gitmodules to exclude list

Rocprofiler-register needs to clone or update submodules but
the tarball build excludes .git files to begin with.
This causes a git error during the build when trying to use
submodule update. If the .gitmodules file does not exist
it will clone a fresh copy of the submodules.

bin/create_release_tarball_excludes

@@ -17,6 +17,7 @@ ROCgdb/sim
 flang/test
 hcc
 .git
+.gitmodules
 llgo
 lldb
 build