A continuation of previous fix for malloc hooks which got removed
from the new glibc library.
The pre-compiled jemalloc has definitions which interpose hooks
in glibc leading to linking errors with multiple hook definitions.
A simple fix is to skip doing the workaround when using jemalloc
from pre-compiled libraries.
This will likely be revisited in the future, but for now it is
important to fix compilation errors for developers.
Starting from GLibC 2.34, deprecated `__malloc_hook` & co. have been
removed from headers, while still present in the shared library itself.
This means that it is no more possible to build Blender with USD 22.03
on recent linux systems.
While USD 22.08 has a fix to this issue, it is unlikely to be upgraded
for Blender 3.4, and definitely not for Blender 3.3.
This commit ensures Blender can build with USD 22.03 and glibc >= 2.34.
Ref.: T99618,
https://devtalk.blender.org/t/building-blender-on-linux-using-glibc-2-34-raises-linking-errors-from-the-usd-library/24185
Patch by @brecht, many thanks.
Checking for the existence of and using __GLIBC_PREREQ can't be done in the
same conditional.
Contributed by listout.
Differential Revision: https://developer.blender.org/D15690
Don't use -ffast-math functions for libc compatibility implementation, since
then the function ends up calling itself. This may not be ideal for performance
but should be insignificant in practice.
On Linux, precompiled libraries may be made with a glibc version that is
incompatible with the system libraries that Blender is built on. To solve
this we add a few -ffast-math symbols that can be missing.
Differential Revision: https://developer.blender.org/D6930
