Allow for more configurable build

Author: DavidZemon

Makefile

@@ -18,12 +18,13 @@ ROOT=$(shell pwd)
 CURSES=
 CURSES_PREFIX=$(HOME)
 ifeq ($(CROSS),)
-  BUILD=$(ROOT)/../build
+  BUILD?=$(ROOT)/../build
+  PREFIX?=/opt/parallax
   CFGCROSS=
   CROSSCC=gcc
 else
-  BUILD=$(ROOT)/../build-$(CROSS)
-  PREFIX=/opt/parallax-$(CROSS)
+  BUILD?=$(ROOT)/../build-$(CROSS)
+  PREFIX?=/opt/parallax-$(CROSS)
   ifeq ($(CROSS),win32)
     CROSS_TARGET=i586-mingw32msvc
     CFGCROSS=--host=$(CROSS_TARGET)
@@ -45,8 +46,6 @@ else
   endif
 endif
 
-PREFIX?=/opt/parallax
-
 ECHO=echo
 RM=rm
 CD=cd