Fix opam unable to find executables on systems where users belong to …

…more than 32 groups when opam is built using musl libc

Details of the issue in musl described in https://www.openwall.com/lists/musl/2021/07/03/1

.gitignore

@@ -83,8 +83,6 @@ src/client/no-git-version
 src/core/developer
 src/manifest/dune
 src/manifest/install.inc
-src/stubs/libacl/dune
-src/stubs/libacl/c-libraries.sexp
 src/stubs/win32/cc64
 src/stubs/win32/dune
 src/stubs/c-flags.sexp

Makefile

@@ -96,7 +96,7 @@ clean:
 distclean: clean clean-ext
 	rm -rf autom4te.cache bootstrap
 	rm -f Makefile.config config.log config.status aclocal.m4
-	rm -f src/*.META src/*/.merlin src/manifest/dune src/manifest/install.inc src/stubs/libacl/dune src/stubs/win32/dune src/stubs/win32/cc64 src/ocaml-flags-configure.sexp src/stubs/libacl/c-libraries.sexp
+	rm -f src/*.META src/*/.merlin src/manifest/dune src/manifest/install.inc src/stubs/win32/dune src/stubs/win32/cc64 src/ocaml-flags-configure.sexp
 	rm -f src/client/linking.sexp src/stubs/c-flags.sexp src/core/developer src/core/version
 
 OPAMINSTALLER_FLAGS = --prefix "$(call CYGPATH,$(DESTDIR)$(prefix))"