Many check_debug regressions

[Paolo Carlini]

.. these are the experimental/string_view fails:

FAIL: experimental/string_view/element_access/char/1.cc (test for excess 
errors)
WARNING: experimental/string_view/element_access/char/1.cc compilation 
failed to produce executable
FAIL: experimental/string_view/element_access/char/2.cc (test for excess 
errors)
WARNING: experimental/string_view/element_access/char/2.cc compilation 
failed to produce executable
FAIL: experimental/string_view/element_access/char/front_back.cc (test 
for excess errors)
WARNING: experimental/string_view/element_access/char/front_back.cc 
compilation failed to produce executable
FAIL: experimental/string_view/element_access/wchar_t/1.cc (test for 
excess errors)
WARNING: experimental/string_view/element_access/wchar_t/1.cc 
compilation failed to produce executable
FAIL: experimental/string_view/element_access/wchar_t/2.cc (test for 
excess errors)
WARNING: experimental/string_view/element_access/wchar_t/2.cc 
compilation failed to produce executable
FAIL: experimental/string_view/element_access/wchar_t/front_back.cc 
(test for excess errors)
WARNING: experimental/string_view/element_access/wchar_t/front_back.cc 
compilation failed to produce executable
FAIL: experimental/string_view/requirements/explicit_instantiation/1.cc 
(test for excess errors)
FAIL: 
experimental/string_view/requirements/explicit_instantiation/char/1.cc 
(test for excess errors)
FAIL: 
experimental/string_view/requirements/explicit_instantiation/char16_t/1.cc 
(test for excess errors)
FAIL: 
experimental/string_view/requirements/explicit_instantiation/char32_t/1.cc 
(test for excess errors)
FAIL: 
experimental/string_view/requirements/explicit_instantiation/wchar_t/1.cc (test 
for excess errors)

Paolo.