Relax unix compile.test to check the expected file exists

When cross compiling between two systems that use different
program file formats (such as PECOFF vs ELF) -x cannot be
relied upon, so -f should be used instead.

Change-Id: I4c80646b2b1fbdd6072589d4d9e852adda83424a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

config.tests/unix/compile.test

@@ -76,7 +76,7 @@ else
     $MAKE >/dev/null 2>&1
 fi
 
-( [ -x "$EXE" ] || [ -x "${EXE}.exe" ] ) && SUCCESS=yes
+( [ -f "$EXE" ] || [ -f "${EXE}.exe" ] ) && SUCCESS=yes
 
 # done
 if [ "$SUCCESS" != "yes" ]; then