Improve bzip2 build system

This patch makes a number of improvements to the bzip2 build system:

 * Remove the BIGFILE variable that was used to force largefile
   support. Now, the user of the Makefile is supposed to pass
   -D_FILE_OFFSET_BITS=64 when largefile support is desired.

 * Use override CFLAGS += so that additional CFLAGS can be passed on
   the command line.

 * Removed "forced" CFLAGS -O2, -g and -Winline. We don't want them by
   default, and want the build system to use its own ones.

 * When creating the symbolic links bzegrep, bzfgrep, bzless and
   bzcmp, don't link them to an absolute path, or they'll point to
   some path on the build machine.

 * Provide an install target for the shared library, which creates the
   appropriate symbolic links.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/Makefile
===================================================================
--- a/Makefile
+++ b/Makefile
@@ -20,8 +20,7 @@
 RANLIB=ranlib
 LDFLAGS=
 
-BIGFILES=-D_FILE_OFFSET_BITS=64
-CFLAGS=-Wall -Winline -O2 -g $(BIGFILES)
+override CFLAGS += -Wall
 
 # Where you want it installed when you do 'make install'
 PREFIX=/usr/local
@@ -90,14 +89,14 @@
 	cp -f libbz2.a $(PREFIX)/lib
 	chmod a+r $(PREFIX)/lib/libbz2.a
 	cp -f bzgrep $(PREFIX)/bin/bzgrep
-	ln -s -f $(PREFIX)/bin/bzgrep $(PREFIX)/bin/bzegrep
-	ln -s -f $(PREFIX)/bin/bzgrep $(PREFIX)/bin/bzfgrep
+	ln -s -f bzgrep $(PREFIX)/bin/bzegrep
+	ln -s -f bzgrep $(PREFIX)/bin/bzfgrep
 	chmod a+x $(PREFIX)/bin/bzgrep
 	cp -f bzmore $(PREFIX)/bin/bzmore
-	ln -s -f $(PREFIX)/bin/bzmore $(PREFIX)/bin/bzless
+	ln -s -f bzmore $(PREFIX)/bin/bzless
 	chmod a+x $(PREFIX)/bin/bzmore
 	cp -f bzdiff $(PREFIX)/bin/bzdiff
-	ln -s -f $(PREFIX)/bin/bzdiff $(PREFIX)/bin/bzcmp
+	ln -s -f bzdiff $(PREFIX)/bin/bzcmp
 	chmod a+x $(PREFIX)/bin/bzdiff
 	cp -f bzgrep.1 bzmore.1 bzdiff.1 $(PREFIX)/man/man1
 	chmod a+r $(PREFIX)/man/man1/bzgrep.1
Index: b/Makefile-libbz2_so
===================================================================
--- a/Makefile-libbz2_so
+++ b/Makefile-libbz2_so
@@ -23,8 +23,7 @@
 
 SHELL=/bin/sh
 CC=gcc
-BIGFILES=-D_FILE_OFFSET_BITS=64
-CFLAGS=-fpic -fPIC -Wall -Winline -O2 -g $(BIGFILES)
+override CFLAGS += -fpic -fPIC -Wall
 
 OBJS= blocksort.o  \
       huffman.o    \
@@ -37,8 +36,11 @@
 all: $(OBJS)
 	$(CC) -shared -Wl,-soname -Wl,libbz2.so.1.0 -o libbz2.so.1.0.6 $(OBJS)
 	$(CC) $(CFLAGS) -o bzip2-shared bzip2.c libbz2.so.1.0.6
-	rm -f libbz2.so.1.0
-	ln -s libbz2.so.1.0.6 libbz2.so.1.0
+
+install:
+	install -m 0755 -D libbz2.so.1.0.6 $(PREFIX)/lib/libbz2.so.1.0.6
+	ln -sf libbz2.so.1.0.6 $(PREFIX)/lib/libbz2.so
+	ln -sf libbz2.so.1.0.6 $(PREFIX)/lib/libbz2.so.1.0
 
 clean: 
 	rm -f $(OBJS) bzip2.o libbz2.so.1.0.6 libbz2.so.1.0 bzip2-shared