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

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

lib/cpp/src/thrift/concurrency/Mutex.h

@@ -20,6 +20,7 @@
 #ifndef _THRIFT_CONCURRENCY_MUTEX_H_
 #define _THRIFT_CONCURRENCY_MUTEX_H_ 1
 
+#include <cstdint>
 #include <memory>
 #include <thrift/TNonCopyable.h>