Workaround mimalloc __THROW decl in cpp files

Summary: This fixes an issue with the 3.15 build. When we include the mimalloc header in our cinderx/python.h we end up getting lots of build errors in C++ files. These are from the presence of `__THROW` being defined which mimalloc is checking for and using for `mimalloc_throw`. So we just undefine it away as we don't really care about this.

Reviewed By: jbower-fb

Differential Revision: D88178338

fbshipit-source-id: 2612373dc341599500986d491c58f39e1e6a5715

Author: DinoV

cinderx/python.h

@@ -10,6 +10,11 @@
 #include <Python.h>
 
 #if PY_VERSION_HEX >= 0x030E0000
+#ifdef __THROW
+// mi_decl_throw is defined to be __THROW and breaks in C++ files.
+#undef __THROW
+#define __THROW
+#endif
 #include "internal/pycore_mimalloc.h"
 #endif