libstdc++: Enable _GLIBCXX_ASSERTIONS by default for -O0 [PR112808]
Too many users don't know about -D_GLIBCXX_ASSERTIONS and so are missing
valuable checks for C++ standard library preconditions. This change
enables libstdc++ assertions by default when compiling with -O0 so that
we diagnose more bugs by default.
When users enable optimization we don't add the assertions by default
(because they have non-zero overhead) so they still need to enable them
manually.
For users who really don't want the assertions even in unoptimized
builds, defining _GLIBCXX_NO_ASSERTIONS will prevent them from being
enabled automatically.
libstdc++-v3/ChangeLog:
PR libstdc++/112808
* doc/xml/manual/using.xml (_GLIBCXX_ASSERTIONS): Document
implicit definition for -O0 compilation.
(_GLIBCXX_NO_ASSERTIONS): Document.
* doc/html/manual/using_macros.html: Regenerate.
* include/bits/c++config [!__OPTIMIZE__] (_GLIBCXX_ASSERTIONS):
Define for unoptimized builds.