Add comment explaining why .dll is not present in DYNAMICLIB_ENDINGS.

emcc

@@ -60,7 +60,7 @@ OBJC_ENDINGS = ('.m',)
 OBJCXX_ENDINGS = ('.mm',)
 SOURCE_ENDINGS = C_ENDINGS + CXX_ENDINGS + OBJC_ENDINGS + OBJCXX_ENDINGS
 BITCODE_ENDINGS = ('.bc', '.o', '.obj')
-DYNAMICLIB_ENDINGS = ('.dylib', '.so')
+DYNAMICLIB_ENDINGS = ('.dylib', '.so') # Windows .dll suffix is not included in this list, since those are never linked to directly on the command line.
 STATICLIB_ENDINGS = ('.a',)
 ASSEMBLY_ENDINGS = ('.ll',)
 HEADER_ENDINGS = ('.h', '.hxx', '.hpp', '.hh', '.H', '.HXX', '.HPP', '.HH')