The patches allow for MODEL, DMD (compiler for the library) and
DDOC (documentation generator) to be overriden on the command line.
--- src/dmd/posix.mak
+++ src/dmd/posix.mak
@@ -49,7 +49,7 @@
 TK=tk
 ROOT=root
 
-MODEL=32
+MODEL?=32
 ifneq (x,x$(MODEL))
     MODEL_FLAG=-m$(MODEL)
 endif
--- src/druntime/posix.mak
+++ src/druntime/posix.mak
@@ -37,7 +37,7 @@
 DOCDIR=doc
 IMPDIR=import
 
-MODEL=32
+MODEL?=32
 override PIC:=$(if $(PIC),-fPIC,)
 
 DFLAGS=-m$(MODEL) -O -release -inline -w -Isrc -Iimport -property $(PIC)
--- src/phobos/posix.mak
+++ src/phobos/posix.mak
@@ -149,7 +149,7 @@
 endif
 
 # Set DDOC, the documentation generator
-DDOC=$(DMD)
+DDOC?=$(DMD)
 
 # Set LIB, the ultimate target
 ifeq (,$(findstring win,$(OS)))