warning: 'mallinfo' is deprecated (memory_usage.cc)

[cz4rs]

Describe the bug
After upgrading to Ubuntu 21.04 and clang 12, following warning appears during compilation:
/vt/src/vt/utils/memory/memory_usage.cc:149:26: warning: 'mallinfo' is deprecated [-Wdeprecated-declarations]

Compilation line:

 vt  build  /bin/clang++ -DBROTLI_SHARED_COMPILATION -DJSON_USE_IMPLICIT_CONVERSIONS=1 -I../lib/CLI -Idebug -I../src -I../lib/json/include -I../lib/brotli/c/include -I../lib/libfort/lib -I../lib/context/src -Ilib/context -Ilib/checkpoint/src -I../lib/checkpoint/src -I../lib/detector/src -isystem ../lib/fmt/include  -Wall -pedantic -Wshadow -Wno-unknown-pragmas -Wsign-compare -ftemplate-backtrace-limit=100 -fsanitize=undefined  -ftemplate-depth=900 -DCLI11_EXPERIMENTAL_OPTIONAL=0 -g -fcolor-diagnostics -fPIC -std=c++14 -o src/CMakeFiles/vt.dir/vt/utils/memory/memory_usage.cc.o -c /vt/src/vt/utils/memory/memory_usage.cc
/vt/src/vt/utils/memory/memory_usage.cc:149:26: warning: 'mallinfo' is deprecated [-Wdeprecated-declarations]
    struct mallinfo mi = mallinfo();
                         ^
/usr/include/malloc.h:118:48: note: 'mallinfo' has been explicitly marked deprecated here
extern struct mallinfo mallinfo (void) __THROW __MALLOC_DEPRECATED;
                                               ^

glibc version:

 ldd --version 
ldd (Ubuntu GLIBC 2.33-0ubuntu5) 2.33

Expected behavior
Use mallinfo2 instead. See the fix in llvm for reference.

[cz4rs]

TODO: re-enable -Werror flag in Ubuntu 22.04 builds after the warning is fixed.