Fixed bug 4154 - Fix three empty variable tests in configure

Zack Middleton

Running top-level SDL configure on macOS 10.11 resulted in the errors below because automake removed the brackets about the tests.

./configure: line 15756: : command not found
./configure: line 15759: -Iinclude -I/Users/zack/SDL/include -idirafter /Users/zack/SDL/src/video/khronos : No such file or directory
./configure: line 15763: : command not found

configure

@@ -15753,14 +15753,14 @@ EXTRA_LDFLAGS="$BASE_LDFLAGS"
 #done
 SDL_CFLAGS="$BASE_CFLAGS"
 SDL_LIBS="-lSDL2"
-if  "$BASE_LDFLAGS" != "" ; then
+if test "x$BASE_LDFLAGS" != x; then
     SDL_LIBS="$SDL_LIBS $BASE_LDFLAGS"
 fi
-if  "$EXTRA_CFLAGS" != "" ; then
+if test "x$EXTRA_CFLAGS" != x; then
     CPPFLAGS="$CPPFLAGS $EXTRA_CFLAGS"
     CFLAGS="$CFLAGS $EXTRA_CFLAGS"
 fi
-if  "$EXTRA_LDFLAGS" != "" ; then
+if test "x$EXTRA_LDFLAGS" != x; then
     LDFLAGS="$LDFLAGS $EXTRA_LDFLAGS"
 fi
 

configure.in

@@ -124,14 +124,14 @@ EXTRA_LDFLAGS="$BASE_LDFLAGS"
 #done
 SDL_CFLAGS="$BASE_CFLAGS"
 SDL_LIBS="-lSDL2"
-if [ "$BASE_LDFLAGS" != "" ]; then
+if test "x$BASE_LDFLAGS" != x; then
     SDL_LIBS="$SDL_LIBS $BASE_LDFLAGS"
 fi
-if [ "$EXTRA_CFLAGS" != "" ]; then
+if test "x$EXTRA_CFLAGS" != x; then
     CPPFLAGS="$CPPFLAGS $EXTRA_CFLAGS"
     CFLAGS="$CFLAGS $EXTRA_CFLAGS"
 fi
-if [ "$EXTRA_LDFLAGS" != "" ]; then
+if test "x$EXTRA_LDFLAGS" != x; then
     LDFLAGS="$LDFLAGS $EXTRA_LDFLAGS"
 fi