https://github.com/aquynh/capstone/issues/1311

Avoid double DESTDIR in install.
--- a/Makefile
+++ b/Makefile
@@ -75,4 +75,4 @@ LIBDIRARCH ?= lib
 #LIBDIRARCH ?= lib64
-LIBDIR = $(DESTDIR)$(PREFIX)/$(LIBDIRARCH)
-BINDIR = $(DESTDIR)$(PREFIX)/bin
+LIBDIR = $(PREFIX)/$(LIBDIRARCH)
+BINDIR = $(PREFIX)/bin