Because of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71962, and
because marking constExpr() as __attribute__((no_sanitize_undefined))
doesn't fix a thing, we opted to disable the triggering parts of
constExpr() from all GCC builds.
This is, of course, unfortunate, since it meaningfully reduces
compile-time coverage in the general case for a rather obscure build
type most won't ever use.
While GCC doesn't give us a predefined macro to check for in the .cpp
file, the cmake build system knows whether we use ubsan, so just
define a macro of our own.
As a drive-by, simplify GCC detection by using Q_CC_GCC_ONLY.
Amends de6a004bc5.
Pick-to: 6.7 6.5 6.2
Task-number: QTBUG-101307
Change-Id: I4be5bd103b9d2386b2ac9fd22e0c34f9c63fee04
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
564be117fe