patch 8.1.2397: should not define __USE_XOPEN

Problem:    Should not define __USE_XOPEN. _XOPEN_SOURCE is not needed for
            Android.
Solution:   Remove __USE_XOPEN and adjust #ifdefs. (Ozaki Kiichi,
            closes #5322)
diff --git a/src/vim.h b/src/vim.h
index 19c19de..68e2de1 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -36,7 +36,7 @@
     Error: configure did not run properly.  Check auto/config.log.
 # endif
 
-# if defined(__gnu_linux__) || defined(__CYGWIN__)
+# if (defined(__linux__) && !defined(__ANDROID__)) || defined(__CYGWIN__)
 // Needed for strptime().  Needs to be done early, since header files can
 // include other header files and end up including time.h, where these symbols
 // matter for Vim.
@@ -44,9 +44,6 @@
 #  ifndef _XOPEN_SOURCE
 #   define _XOPEN_SOURCE    700
 #  endif
-#  ifndef __USE_XOPEN
-#   define __USE_XOPEN
-#  endif
 # endif
 
 // for INT_MAX, LONG_MAX et al.