Added PowerPC detection code for linux

contrib/powerpc-vsx/linux.c

@@ -0,0 +1,57 @@
+/* contrib/powerpc-vsx/linux.c
+ *
+ * Copyright (c) 2016 Glenn Randers-Pehrson
+ * Written by Vadim Barkov, 2017.
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ *
+ * SEE contrib/powerpc-vsx/README before reporting bugs
+ *
+ * STATUS: COMPILED
+ * BUG REPORTS: png-mng-implement@sourceforge.net
+ *
+ * png_have_vsx implemented for Linux by reading the widely available
+ * pseudo-file /proc/cpuinfo. Result is cached so if function will be called
+ * multiple times only one reading is perfomed.
+ *
+ * This code is strict ANSI-C and is probably moderately portable; it does
+ * however use <stdio.h> and it assumes that /proc/cpuinfo is never localized.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "png.h"
+
+#ifndef MAXLINE
+#  define MAXLINE 1024
+#endif
+
+static int
+png_have_vsx(png_structp png_ptr)
+{
+   FILE *f;
+
+   const char *string = "altivec supported";
+   char input[MAXLINE];
+   char *token = NULL;
+
+   f = fopen("/proc/cpuinfo", "r");
+   if (f != NULL)
+   {
+      memset(input,0,MAXLINE);
+      while(fgets(input,MAXLINE,f) != NULL)
+      {
+         token = strstr(input,string);
+	 if(token != NULL)
+	    return cachedResult;
+      }
+   }
+#ifdef PNG_WARNINGS_SUPPORTED
+   else
+      png_warning(png_ptr, "/proc/cpuinfo open failed");
+#endif
+   return cachedResult;
+}