ENGINES: Add "PPC" to the advanced detector gray list

Files named "PPC" are relatively common for mac games around
the mid-90s (when Apple transitionned from x86 to PPC cpus).
This for example prevent detecting the mac versions of Broken
Sword 1 as unknown director games.

engines/advancedDetector.cpp

@@ -815,6 +815,7 @@ static const char *grayList[] = {
 	"start.exe",
 	"item.dat",
 	"abc.exe",
+	"ppc",
 	0
 };