update libpcp to lastest main (scp-fs2open#6963)

This should fix build issues on ARM64 Windows.

Note that the project name changed from libpcp to libpcpnatpmp and is in
active development again after a multi-year period of inactivity. There
are currently no versioned releases. This is hash b5fe5e2.

Author: notimaginative

code/CMakeLists.txt

@@ -59,7 +59,7 @@ endif()
 
 target_link_libraries(code PUBLIC libRocket)
 
-target_link_libraries(code PUBLIC pcp)
+target_link_libraries(code PUBLIC pcpnatpmp)
 
 target_link_libraries(code PUBLIC parsers)
 

code/network/multi_portfwd.cpp

@@ -15,7 +15,7 @@
 #include <netdb.h>
 #endif
 
-#include "pcp.h"
+#include "pcpnatpmp.h"
 
 #include "cmdline/cmdline.h"
 #include "io/timer.h"

lib/CMakeLists.txt

@@ -39,7 +39,7 @@ endif()
 
 include(libRocket.cmake)
 
-add_subdirectory(libpcp)
+add_subdirectory(libpcpnatpmp)
 
 include(antlr4.cmake)