For ELF platforms with a GCC-compatible compiler, the QElfParser has
been ignoring the .rodata section ever since Qt 5.0 commit
7443895857 ("Remove support for Qt 4 style
plugins"). That change removed handling of return value
QElfParser::NoQtSection from the ELF parser, which meant that the
plugins without a .qtmetadata section were never considered plugins. In
other words, for those systems, the __attribute__ macro is mandatory.
For systems with a GCC-incompatible compiler, there were only two in Qt
5.x's lifetime: Oracle/Sun Solaris with SunCC and IBM AIX with IBM xlC
compiler. Neither compiler supports C++17 according to [1], so they
can't be in use in Qt 6. IBM xlC now comes with a Clang-based front-end
for users who need Qt 6 and the OpenIndiana distribution of Open Source
Solaris has been using GCC since 2012.
So make the macros mandatory from now on.
[1] https://en.cppreference.com/w/cpp/compiler_support#C.2B.2B17_features
Change-Id: I42eb903a916645db9900fffd16a443745446cc64
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
42ec48d819