Use dylib extension for iOS installs, too.

Reported by Andrey Filipenkov. #1336

Makefile

@@ -110,7 +110,7 @@ else
 endif
 TARGET_SYS?= $(HOST_SYS)
 
-ifeq (Darwin,$(TARGET_SYS))
+ifneq (,$(filter $(TARGET_SYS),Darwin iOS))
   INSTALL_SONAME= $(INSTALL_DYLIBNAME)
   INSTALL_SOSHORT1= $(INSTALL_DYLIBSHORT1)
   INSTALL_SOSHORT2= $(INSTALL_DYLIBSHORT2)