Move SC_PRIsizet to compat.h

Define the printf format macro for size_t in compat.h so that it can be
used from anywhere.

PR #3005 <https://github.com/Genymobile/scrcpy/pull/3005>

app/src/compat.h

@@ -8,8 +8,10 @@
 
 #ifndef __WIN32
 # define PRIu64_ PRIu64
+# define SC_PRIsizet "zu"
 #else
 # define PRIu64_ "I64u"  // Windows...
+# define SC_PRIsizet "Iu"
 #endif
 
 // In ffmpeg/doc/APIchanges:

app/src/util/process.h

@@ -12,8 +12,6 @@
 # include <winsock2.h>
 # include <windows.h>
 # define SC_PRIexitcode "lu"
-// <https://stackoverflow.com/a/44383330/1987178>
-# define SC_PRIsizet "Iu"
 # define SC_PROCESS_NONE NULL
 # define SC_EXIT_CODE_NONE -1UL // max value as unsigned long
   typedef HANDLE sc_pid;
@@ -23,7 +21,6 @@
 #else
 
 # include <sys/types.h>
-# define SC_PRIsizet "zu"
 # define SC_PRIexitcode "d"
 # define SC_PROCESS_NONE -1
 # define SC_EXIT_CODE_NONE -1