These testcases were failing on nios2-elf, which defaults to
-fno-delete-null-pointer-checks.

2020-01-24  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/testsuite/
	* g++.dg/cpp0x/constexpr-odr1.C: Add -fdelete-null-pointer-checks.
	* g++.dg/cpp0x/constexpr-odr2.C: Likewise.
	* g++.dg/cpp0x/nontype4.C: Likewise.
	* g++.dg/cpp1y/constexpr-new.C: Likewise.
	* g++.dg/cpp1y/new1.C: Likewise.
	* g++.dg/cpp1y/new2.C: Likewise.
	* g++.dg/cpp2a/constexpr-dynamic11.C: Likewise.
	* g++.dg/cpp2a/constexpr-dynamic17.C: Likewise.
	* g++.dg/cpp2a/constexpr-dynamic4.C: Likewise.
	* g++.dg/cpp2a/constexpr-new1.C: Likewise.
	* g++.dg/cpp2a/constexpr-new10.C: Likewise.
	* g++.dg/cpp2a/constexpr-new2.C: Likewise.
	* g++.dg/cpp2a/constexpr-new3.C: Likewise.
	* g++.dg/cpp2a/constexpr-new4.C: Likewise.
	* g++.dg/cpp2a/constexpr-new8.C: Likewise.
	* g++.dg/cpp2a/constexpr-new9.C: Likewise.
	* g++.dg/cpp2a/nontype-class1.C: Likewise.