Format preprocessor macros more consistently

Within the libjpeg API code, it seems to be more the convention than not
to separate the macro name and value by two or more spaces, which
improves general readability.  Making this consistent across all of
libjpeg-turbo is less about my individual preferences and more about
making it easy to automatically detect variations from our chosen
formatting convention.  I intend to release the script I'm using to
validate this stuff, once it matures and stabilizes a bit.

jcstest.c

@@ -35,10 +35,10 @@
 #include <setjmp.h>
 
 #ifndef JCS_EXTENSIONS
-#define JCS_EXT_RGB 6
+#define JCS_EXT_RGB  6
 #endif
 #if !defined(JCS_EXTENSIONS) || !defined(JCS_ALPHA_EXTENSIONS)
-#define JCS_EXT_RGBA 12
+#define JCS_EXT_RGBA  12
 #endif
 
 static char lasterror[JMSG_LENGTH_MAX] = "No error";