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.
diff --git a/jdhuff.c b/jdhuff.c
index 003cee7..84b9b71 100644
--- a/jdhuff.c
+++ b/jdhuff.c
@@ -491,7 +491,7 @@
 #define AVOID_TABLES
 #ifdef AVOID_TABLES
 
-#define NEG_1 ((unsigned int)-1)
+#define NEG_1  ((unsigned int)-1)
 #define HUFF_EXTEND(x, s) \
   ((x) + ((((x) - (1 << ((s) - 1))) >> 31) & (((NEG_1) << (s)) + 1)))
 
@@ -753,7 +753,7 @@
  * this module, since we'll just re-assign them on the next call.)
  */
 
-#define BUFSIZE (DCTSIZE2 * 8)
+#define BUFSIZE  (DCTSIZE2 * 8)
 
 METHODDEF(boolean)
 decode_mcu(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)