THRIFT-5842: Add missing cstdint include for int64_t in Mutex.h

[kou]

Client: cpp

GCC 15 (not released yet) requires #include <cstdint> for int64_t but lib/cpp/src/thrift/concurrency/Mutex.h doesn't have it. So we can't build Thrift with GCC 15:

[80/359] Building CXX object lib/cpp/CMakeFiles/thrift.dir/src/thrift/transport/TSSLServerSocket.cpp.o
FAILED: lib/cpp/CMakeFiles/thrift.dir/src/thrift/transport/TSSLServerSocket.cpp.o
/bin/g++-15 -DBOOST_ALL_DYN_LINK -DBOOST_TEST_DYN_LINK -DTHRIFT_STATIC_DEFINE -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/kou/work/cpp/thrift.kou.build/lib/cpp -I/home/kou/work/cpp/thrift.kou/lib/cpp -I/home/kou/work/cpp/thrift.kou.build -I/home/kou/work/cpp/thrift.kou/lib/cpp/src -g -std=c++11 -MD -MT lib/cpp/CMakeFiles/thrift.dir/src/thrift/transport/TSSLServerSocket.cpp.o -MF lib/cpp/CMakeFiles/thrift.dir/src/thrift/transport/TSSLServerSocket.cpp.o.d -o lib/cpp/CMakeFiles/thrift.dir/src/thrift/transport/TSSLServerSocket.cpp.o -c /home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/transport/TSSLServerSocket.cpp
In file included from /home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/transport/TServerSocket.h:25,
                 from /home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/transport/TSSLServerSocket.h:23,
                 from /home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/transport/TSSLServerSocket.cpp:21:
/home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/concurrency/Mutex.h:47:26: error: 'int64_t' has not been declared
   47 |   virtual bool timedlock(int64_t milliseconds) const;
      |                          ^~~~~~~
/home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/concurrency/Mutex.h:25:1: note: 'int64_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
   24 | #include <thrift/TNonCopyable.h>
  +++ |+#include <cstdint>
   25 |
/home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/concurrency/Mutex.h:60:29: error: 'int64_t' has not been declared
   60 |   Guard(const Mutex& value, int64_t timeout = 0) : mutex_(&value) {
      |                             ^~~~~~~
/home/kou/work/cpp/thrift.kou/lib/cpp/src/thrift/concurrency/Mutex.h:60:29: note: 'int64_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'

See also: apache/arrow#45096

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