Small "syntax" issue with xlc compiler and version 1.5.28

Hi.

I just noticed the recent updates - thanks!

During the build on AIX, using xlc as compiler I had a 'textual' syntax 
issue that I was able to resolve with:
(as 1.5.28 and 1.6.28 were equal and showing how I patched 1.5.28)

michael@x071:[/data/prj/aixtools/libpng]diff -u 
./src/libpng-1.6.28/contrib/libtests/pngvalid.c ./src/libpng-1.5.28/contri>
--- ./src/libpng-1.6.28/contrib/libtests/pngvalid.c     2017-01-05 
13:52:09 +0000
+++ ./src/libpng-1.5.28/contrib/libtests/pngvalid.c     2017-01-12 
13:37:45 +0000
@@ -7742,13 +7742,12 @@
            * NOTE: this number only affects the internal limit check in 
pngvalid,
            * it has no effect on the limits applied to the libpng values.
            */
-         that->pm->limit += pow(
-#        if DIGITIZE
-            2.0
-#        else
-            1.0
-#        endif
-            /255, data.gamma);
+         that->pm->limit += pow( 2.0/255, data.gamma);
+#if     DIGITIZE
+           that->pm->limit += pow( 2.0/255, data.gamma);
+#       else
+            that->pm->limit += pow( 1.0/255, data.gamma);
+#       endif
        }
     }

Without the patch I get:

         source='../src/libpng-1.5.28/contrib/libtests/pngvalid.c' 
object='contrib/libtests/pngvalid.o' libtool=no  DEPDIR=.deps 
depmode=xlc /bin/sh ../src/libpng-1.5.28/depcomp  xlc_r -DHAVE_CONFIG_H 
-I. -I../src/libpng-1.5.28    -I/opt/include -I/opt/buildaix/include  
-I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5 -I/opt/buildaix/includes -c 
-o contrib/libtests/pngvalid.o 
../src/libpng-1.5.28/contrib/libtests/pngvalid.c
"../src/libpng-1.5.28/contrib/libtests/pngvalid.c", line 7746.1: 
1506-191 (E) The character # is not a valid C source character.
"../src/libpng-1.5.28/contrib/libtests/pngvalid.c", line 7746.10: 
1506-046 (S) Syntax error.
"../src/libpng-1.5.28/contrib/libtests/pngvalid.c", line 7748.1: 
1506-191 (E) The character # is not a valid C source character.
"../src/libpng-1.5.28/contrib/libtests/pngvalid.c", line 7750.1: 
1506-191 (E) The character # is not a valid C source character.
make: 1254-004 The error code from the last command is 1.


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