MDEV-6149 Include file pcre.h missing in binary dist, meaing I_S plugins can't be built

when the bundled pcre is used, install its pcre.h in mysql/private/

pcre/CMakeLists.txt

@@ -513,4 +513,6 @@ IF(PCRE_SHOW_REPORT)
   MESSAGE(STATUS "")
 ENDIF(PCRE_SHOW_REPORT)
 
+INSTALL(FILES ${CMAKE_BINARY_DIR}/pcre/pcre.h DESTINATION ${INSTALL_INCLUDEDIR}/private COMPONENT Development)
+
 # end CMakeLists.txt