FTBFS when cross compiling with gcc11

[1/55] Compiling C++ object src/libmedialibrary.a.p/Album.cpp.obj
FAILED: src/libmedialibrary.a.p/Album.cpp.obj 
i686-w64-mingw32-g++ -Isrc/libmedialibrary.a.p -Isrc -I../src -I. -I.. -Iinclude -I../include -I/home/chouquette/dev/vlc/contrib/i686-w64-mingw32/include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -Wextra -std=c++14 -g -DHAVE_CONFIG_H=1 -D__MSVCRT_VERSION__=0x700 -D_WIN32_WINNT=0x0601 -DWINVER=0x0601 -MD -MQ src/libmedialibrary.a.p/Album.cpp.obj -MF src/libmedialibrary.a.p/Album.cpp.obj.d -o src/libmedialibrary.a.p/Album.cpp.obj -c ../src/Album.cpp
In file included from ../src/utils/SWMRLock.h:25,
                 from ../src/database/SqliteConnection.h:31,
                 from ../src/database/SqliteTools.h:35,
                 from ../src/database/DatabaseHelpers.h:30,
                 from ../src/Album.h:30,
                 from ../src/Album.cpp:29:
../src/compat/ConditionVariable.h:35:36: error: 'condition_variable' in namespace 'std' does not name a type
   35 |     using ConditionVariable = std::condition_variable;
      |                                    ^~~~~~~~~~~~~~~~~~
../src/compat/ConditionVariable.h:30:1: note: 'std::condition_variable' is defined in header '<condition_variable>'; did you forget to '#include <condition_variable>'?
   29 | #include <condition_variable>
  +++ |+#include <condition_variable>
   30 | 
In file included from ../src/database/SqliteConnection.h:31,
                 from ../src/database/SqliteTools.h:35,
                 from ../src/database/DatabaseHelpers.h:30,
                 from ../src/Album.h:30,
                 from ../src/Album.cpp:29:
../src/utils/SWMRLock.h:56:13: error: 'ConditionVariable' in namespace 'medialibrary::compat' does not name a type
   56 |     compat::ConditionVariable m_cond;
      |             ^~~~~~~~~~~~~~~~~
ninja: build stopped: subcommand failed.

We probably need to split condition_variable and thread detection