CMake: Don't test host system's /proc paths for availability on target. This allows better cross-compilation.

dtool/LocalSetup.cmake

@@ -110,25 +110,15 @@ set(HAVE_IOS_TYPEDEFS 1)
 
 # Can we read the file /proc/self/[*] to determine our
 # environment variables at static init time?
-if(EXISTS "/proc/self/exe")
+if(IS_LINUX)
   set(HAVE_PROC_SELF_EXE 1)
-endif()
-if(EXISTS "/proc/self/maps")
   set(HAVE_PROC_SELF_MAPS 1)
-endif()
-if(EXISTS "/proc/self/environ")
   set(HAVE_PROC_SELF_ENVIRON 1)
-endif()
-if(EXISTS "/proc/self/cmdline")
   set(HAVE_PROC_SELF_CMDLINE 1)
 endif()
-if(EXISTS "/proc/curproc/file")
+if(IS_FREEBSD)
   set(HAVE_PROC_CURPROC_FILE 1)
-endif()
-if(EXISTS "/proc/curproc/map")
   set(HAVE_PROC_CURPROC_MAP 1)
-endif()
-if(EXISTS "/proc/curproc/cmdline")
   set(HAVE_PROC_CURPROC_CMDLINE 1)
 endif()