--- mk.config.orig	2008-04-08 03:42:01.000000000 +0900
+++ mk.config	2008-04-25 23:46:59.000000000 +0900
@@ -1,62 +1,62 @@
 #
 # A BSD-compatible install command.
 #
-INSTALL=/usr/ucb/install
+INSTALL?=/usr/ucb/install
 
 #
 # Packaging prefix.
 #
-PREFIX=/usr
+PREFIX?=/usr
 
 #
 # Where to place binaries.
 #
-BINDIR=$(PREFIX)/ucb
+BINDIR?=$(PREFIX)/ucb
 
 #
 # Where to place libraries.
 #
-LIBDIR=$(PREFIX)/ucblib
+LIBDIR?=$(PREFIX)/ucblib
 
 #
 # Where to place ASCII charts and the like.
 #
-PUBDIR=$(PREFIX)/pub
+PUBDIR?=$(PREFIX)/pub
 
 #
 # Where to place manual pages.
 #
-MANDIR=$(PREFIX)/share/man/5man
+MANDIR?=$(PREFIX)/share/man/5man
 
 #
 # Where to place the troff macro packages.
 #
-MACDIR=$(LIBDIR)/doctools/tmac
+MACDIR?=$(LIBDIR)/doctools/tmac
 
 #
 # Where to place the troff font files.
 #
-FNTDIR=$(LIBDIR)/doctools/font
+FNTDIR?=$(LIBDIR)/doctools/font
 
 #
 # Where to place PostScript helper files.
 #
-PSTDIR=$(FNTDIR)/devpost/postscript
+PSTDIR?=$(FNTDIR)/devpost/postscript
 
 #
 # Where to place the nroff terminal description files.
 #
-TABDIR=$(LIBDIR)/doctools/nterm
+TABDIR?=$(LIBDIR)/doctools/nterm
 
 #
 # Where to place troff hyphenation files.
 #
-HYPDIR=$(LIBDIR)/doctools/hyphen
+HYPDIR?=$(LIBDIR)/doctools/hyphen
 
 #
 # Where to place files belonging to the "refer" utility.
 #
-REFDIR=$(LIBDIR)/reftools
+REFDIR?=$(LIBDIR)/reftools
 
 #
 # Define this if you want troff and nroff to be able to process
@@ -73,17 +73,17 @@
 #
 # The C compiler.
 #
-CC=cc
+CC?=cc
 
 #
 # The C++ compiler.
 #
-CCC=c++
+CCC?=c++
 
 #
 # Compiler flags.
 #
-CFLAGS=-O
+CFLAGS?=-O
 
 #
 # C preprocessor flags.
@@ -91,7 +91,7 @@
 # Use -D_GNU_SOURCE for Linux with GNU libc.
 # Use -D_INCLUDE__STDC_A1_SOURCE for HP-UX.
 #
-CPPFLAGS=-D_GNU_SOURCE
+CPPFLAGS?=-D_GNU_SOURCE
 
 #
 # Warning flags for the compiler.
@@ -101,12 +101,12 @@
 #
 # Linker flags.
 #
-LDFLAGS=
+LDFLAGS?=
 
 #
 # Additional libraries to link with.
 #
-LIBS=
+LIBS?=
 
 #
 # A Bourne-compatible shell.