[PR preprocessor/90927] Fixe dependency output

https://gcc.gnu.org/ml/gcc-patches/2019-06/msg01664.html
	libcpp/
	PR preprocessor/90927
	* mkdeps.c (mkdeps::vec::operator[]): Add non-const variant.
	(deps_add_target): Deal with out of order unquoted targets.

	gcc/testsuite/
	* c-c++-common/pr90927.c: New.

From-SVN: r272692