With the new release of the GCC 9 compiler the operation of -Wmissing-attributes warnings has also been extended to aliases: this causes a warnings if the alias has less attributes than its target.
This warnings does not actually indicate a problem in the mimalloc code and you could safely ignore it by adding "-Wno-missing-attributes" to the CFLAGS, however I was not going to use a "hack" to hide the warning when compiling alloc-override .c
So this patch solves the problem simply by using an attribute (present only in GCC> = 9) that copies the attributes of another function, since this attribute is exclusive only for GCC 9 (or later) I had to use a simple precompiler instruction to add the "copy" attribute only with GCC 9.
Red Hat Linux was discontinued by Red Hat in 2003. It would make sense
to address glibc-based Linux distributions rather than Red Hat Linux.
Reference: https://en.wikipedia.org/wiki/Red_Hat_Linux
Indention programs such as clang-format usually rely on the occurrence
of statement terminator, otherwise they are likely confused. The revised
forwarding macros do not contain semicolons character, which is friendly
to indentation or style checkers.
GCC's default visibility is "public" but can be changed to
"hidden" with the argument "-fvisibility=hidden".
Tested with x86_64 / Ubuntu Linux 18.04 LTS:
[before]
$ nm -g -C libmimalloc.so | grep "T " | wc -l
142
[after]
$ nm -g -C libmimalloc.so | grep "T " | wc -l
93
This patch does not change the build on macOS.
