mingw32: merge checks for mingw-w64 and mingw32-runtime >= 3.15 into one

Originally committed as revision 24204 to svn://svn.ffmpeg.org/ffmpeg/trunk
(cherry picked from commit e26011d0f495de1148b8014995cbe923611b6b76)
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
diff --git a/configure b/configure
index 835535f..67cc2f6 100755
--- a/configure
+++ b/configure
@@ -1611,10 +1611,9 @@
         objformat="win32"
         enable dos_paths
         check_cflags -fno-common
-        if ! check_cpp_condition _mingw.h "defined (__MINGW64_VERSION_MAJOR)"; then
-            check_cpp_condition _mingw.h "(__MINGW32_MAJOR_VERSION > 3) || (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
+        check_cpp_condition _mingw.h "defined (__MINGW64_VERSION_MAJOR) || (__MINGW32_MAJOR_VERSION > 3) \
+                                      || (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
                 die "ERROR: MinGW runtime version must be >= 3.15."
-        fi
         ;;
     cygwin*)
         target_os=cygwin