Use secure_getenv for GOMP_DEBUG

Use secure_getenv for GOMP_DEBUG

2017-06-27  Tom de Vries  <tom@codesourcery.com>

	* env.c (parse_unsigned_long_1): Factor out of ...
	(parse_unsigned_long): ... here.
	(parse_int_1): Factor out of ...
	(parse_int): ... here.
	(parse_int_secure): New function.
	(initialize_env): Use parse_int_secure for GOMP_DEBUG.
	* secure_getenv.h: Factor out of ...
	* plugin/plugin-hsa.c: ... here.
	* testsuite/libgomp.oacc-c-c++-common/gomp-debug-env.c: New test.

From-SVN: r249694