Fix duplicate symbols on some Mac builds

[nlslatt]

Describe the bug
Some vt executables and vt-enabled apps get link errors on Mac:

duplicate symbol 'typeinfo name for vt::pool::MemoryPoolEqual<64ll, true>' in:
    src/libvt-debug.a(memory_pool_equal.cc.o)
    src/libvt-debug.a(runnable.cc.o)
duplicate symbol 'typeinfo for vt::pool::MemoryPoolEqual<64ll, true>' in:
    src/libvt-debug.a(memory_pool_equal.cc.o)
    src/libvt-debug.a(runnable.cc.o)
duplicate symbol 'typeinfo name for vt::pool::MemoryPoolEqual<1024ll, true>' in:
    src/libvt-debug.a(memory_pool_equal.cc.o)
    src/libvt-debug.a(runnable.cc.o)
duplicate symbol 'typeinfo for vt::pool::MemoryPoolEqual<1024ll, true>' in:
    src/libvt-debug.a(memory_pool_equal.cc.o)
    src/libvt-debug.a(runnable.cc.o)

This appears to be related to the #include "src/vt/pool/static_sized/memory_pool_equal.cc" line at the end of src/vt/runnable/runnable.cc. That #include is required, but it seems like the build system is also building memory_pool_equal.cc separately due to the .cc extension, which can result in linking errors. Rename memory_pool_equal.cc so that it doesn't get built separately.