testsuite: Adjust dg-error for -fimplicit-constexpr
Some of the new tests were failing with -fimplicit-constexpr. This
patch adjusts the expected diagnostic. Tested with
GXX_TESTSUITE_STDS=98,11,14,17,20,23 make check-c++ RUNTESTFLAGS="--target_board=unix\{,-fimplicit-constexpr\} dg.exp=spaceship-eq3.C"
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-ex1.C: Adjust dg-error.
* g++.dg/cpp23/constexpr-nonlit10.C: Adjust dg-warning.
* g++.dg/cpp23/constexpr-nonlit11.C: Likewise.
* g++.dg/cpp2a/spaceship-eq3.C: Add dg-error.