[C++] jemalloc prepocessor definitions causes unity builds to mix jemalloc and system allocator functions

[felipecrv]

Since jemalloc.h does

#  define malloc je_malloc

when JEMALLOC_MANGLE is defined, we can get this error in CI during an unity build

/arrow/cpp/src/arrow/vendored/ProducerConsumerQueue.h: In constructor 'arrow_vendored::folly::ProducerConsumerQueue<T>::ProducerConsumerQueue(uint32_t)':

/arrow/cpp/src/arrow/vendored/ProducerConsumerQueue.h:82:39: error: 'je_arrow_malloc' is not a member of 'std'; did you mean 'je_arrow_malloc'?

   82 |         records_(static_cast<T*>(std::malloc(sizeof(T) * size))),

      |                                       ^~~~~~

jemalloc_ep-prefix/src/jemalloc_ep/dist/include/jemalloc/jemalloc.h:254:32: note: 'je_arrow_malloc' declared here

  254 |     void JEMALLOC_SYS_NOTHROW *je_malloc(size_t size)

      |                                ^~~~~~~~~

/arrow/cpp/src/arrow/vendored/ProducerConsumerQueue.h: In destructor 'arrow_vendored::folly::ProducerConsumerQueue<T>::~ProducerConsumerQueue()':

/arrow/cpp/src/arrow/vendored/ProducerConsumerQueue.h:106:10: error: 'je_arrow_free' is not a member of 'std'; did you mean 'je_arrow_free'?

  106 |     std::free(records_);

      |          ^~~~

jemalloc_ep-prefix/src/jemalloc_ep/dist/include/jemalloc/jemalloc.h:269:43: note: 'je_arrow_free' declared here

  269 | JEMALLOC_EXPORT void JEMALLOC_SYS_NOTHROW je_free(void *ptr)

      |                                           ^~~~~~~

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[felipecrv]

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