Fix 'g++.dg/cpp26/static_assert1.C' for '-fno-exceptions' configurations

Fix 'g++.dg/cpp26/static_assert1.C' for '-fno-exceptions' configurations

This test case, added in recent commit 6ce952188ab39e303e4f63e474b5cba83b5b12fd
"c++: Implement C++26 P2741R3 - user-generated static_assert messages [PR110348]",
expectedly runs into 'UNSUPPORTED: [...]: exception handling disabled', but
along the way also FAILs a few tests:

    UNSUPPORTED: g++.dg/cpp26/static_assert1.C  -std=gnu++98
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for warnings, line 6)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for warnings, line 51)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for errors, line 52)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for warnings, line 56)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for warnings, line 57)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++11  at line 58 (test for errors, line 57)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  (test for warnings, line 59)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++11  at line 308 (test for errors, line 307)
    UNSUPPORTED: g++.dg/cpp26/static_assert1.C  -std=gnu++11: exception handling disabled
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 6)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 51)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for errors, line 52)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 56)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 57)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++14  at line 58 (test for errors, line 57)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 59)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  at line 257 (test for errors, line 256)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for errors, line 261)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  (test for warnings, line 262)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++14  at line 308 (test for errors, line 307)
    UNSUPPORTED: g++.dg/cpp26/static_assert1.C  -std=gnu++14: exception handling disabled
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 6)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 51)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for errors, line 52)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 56)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 57)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++20  at line 58 (test for errors, line 57)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 59)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  at line 257 (test for errors, line 256)
    FAIL: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for errors, line 261)
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  (test for warnings, line 262)
    [...]
    PASS: g++.dg/cpp26/static_assert1.C  -std=gnu++20  at line 308 (test for errors, line 307)
    UNSUPPORTED: g++.dg/cpp26/static_assert1.C  -std=gnu++20: exception handling disabled

Use an explicit '-fexceptions' to turn this front end test case all-PASS.

	gcc/testsuite/
	* g++.dg/cpp26/static_assert1.C: Fix for '-fno-exceptions'
	configurations.